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Chapter 4 Animal anatomy.

Chapter Objectives

* Identify the points of external anatomy of animal species

* Identify points of skeletal anatomy of animal species

* Understand types of connective tissue and how they differ

* Understand types of muscle and how they differ

* Know the parts and functions of major body systems

An understanding of external and internal anatomy is important in many fields of animal science. It is vital to understand where various cuts of meat originate, why animals have the characteristics they have, and how and why we manage animals in certain ways. Animal scientists in the field of physiology study various aspects of anatomy, depending on their specialty areas. Exercise physiologists may study skeletal, muscular, and respiratory anatomy, as they seek solutions to problems in athletic animals. Muscle physiologists study the skeleton and muscles as they try to solve muscular problems, as well as increase the amount and quality of muscle in meat animals.


The skeleton is composed of various types of connective tissue that provide the structure and form of the body and bind the parts of the body together. When evaluating animals for different purposes, thorough knowledge of the skeleton is important. The alignment of bones, especially in the legs, is vital to the functionality and longevity of the animal. Skeletal structure is inherited, and structural defects can be passed to future generations. Therefore, animals that are more skeletally correct will remain in the milking or breeding herd for a longer period of time.

The axial (acks-e-ahl) skeleton refers to the central skeleton that includes the skull, the vertebral column, and the ribs; the appendicular (ahp-en-dik-yoo-ler) skeleton refers to the limbs and appendages of the body. Differences in skeletal anatomy of avian species and mammals are relatively slight; therefore, differences between avian species and other mammals will be indicated in the definition of the skeletal part. The following are terms that relate to both the axial and appendicular skeletons:

Bone Bone is the hardest connective tissue, and provides structure and form to the body. In birds, the bones are lighter weight and hollow, which allows some birds to fly.

Cartilage (cahr-tuh-ludge) This connective tissue is more flexible than bone, and can be found either on parts of the bone or independent of bone. Ears are examples of cartilage that are independent of bone. The following are the different types of cartilage:

Articular (ahr-tik-yoo-ler) Covers the surface of the bone in some types of joints.


Meniscus (meh-nis-kuhs) Cartilage located between bone surfaces to cushion the surfaces (for example, stifle joint).

Joint Where bones come together. Bodies have a variety of types of joints (see Figure 4-1). The following are the different types of joints:

Arthroidal (ahrth-roy-duhl) A joint in which small oval-shaped bones fit into a depression in a large bone (for example, carpal joint).

Ball and socket Highly movable joints in which the end of one bone is shaped into a ball that fits into a depression (socket) of the other bone in the joint (for example, hip joint).

Hinge Joints that allow movement in only one direction, such as the stifle joint.

Suture (soo-cher) An immovable joint where two bones join (for example, bones of the skull).

Symphysis (sihm-fih-sihs) A type of joint where the two bones meet and work as a single bone, are joined by cartilage, and have limited movement (for example, pelvis).

Trochoid Joints that operate with a pulley-type function, such as the atlas/axial joint.

Ligament (lihg-ah-mehnt) Connective tissue that attaches bone to bone.

Tendon (tehn-dohn) Connective tissue that attaches muscle to bone.

Axial Skeleton

The axial skeleton of avian species and mammals is very similar, so differences in the axial skeleton will be noted with each particular bone. The following are the components of the axial skeleton from the front of the body to the rear:

Skull (skuhl) The skull is the bony structure that provides shape to the head. The following are the bones and regions that make up the skull:

Cranium (kra-ne-uhm) The portion of the skull that surrounds and protects the brain.

Nasal (na--sahl) The bone that creates the bridge of the nose.

Nasal septum (sehp-tuhm) The cartilage that divides the nasal cavity into two structures.

Sinuses (sin-uhs-ehz) Spaces in the skull that are filled with air or fluid.


Vertebral column (ver-te-brahl) The column of bone also known as the backbone or the spine (see Figure 4-2). The vertebral column is made up of many individual vertebra (ver-te-brah). The plural form of vertebra is vertebrae (ver-te-bra). Vertebrae are grouped-based on their location in the vertebral column, and are numbered from the head to the tail. The following list of vertebrae is in order from the skull to the end of the spine:

Cervical (sihr-vih-kahl) The vertebrae that constitute the neck. All mammals have seven cervical vertebrae, regardless of the length of their necks. Cervical vertebrae are numbered C1 through C7, with C1 being nearest the skull. C1 is also called the atlas, and C2 is also called the axis.

Thoracic (thor-ahs-ihck) The vertebrae next to the cervical. Thoracic vertebrae form the external part of the back (or chine), and are attached to the ribs. You can locate the end of the thoracic vertebrae by locating the last rib.

Lumbar (luhm-bahr) The vertebrae following the thoracic. Lumbar vertebrae do not have ribs attached, and are supported by muscle only. The lumbar region is also termed the loin.

Sacral (sa-krahl) The vertebrae following the lumbar. These vertebrae make up the croup or rump (the external term varies with species).

Coccygeal (kohck-sih-je-ahl) Also known as caudal (kaw-duhl) vertebrae, the coccygeal vertebrae are the last in the vertebral column, and make up the tail.

Ribs The paired bones that attach on one side to the thoracic vertebrae, and on the other side to the sternum (ster-nuhm). The sternum is also known as the breastbone (or keel in avian species). Barrel is a common term used to describe the rib and body area.



Appendicular Skeleton

The appendicular skeleton includes the limbs of the

body. In quadrupeds (kwa-droo-pedz)--four-legged animals--the limbs are commonly divided into the forequarter, which includes all parts of the shoulder and front leg, and the hindquarter (hind-kwar-ter), which includes all parts of the hip and hind leg (see Figure 4-3 and Figure 4-4).

Skeleton of the Forequarter

The forequarter carries the majority of the weight of quadrupeds. As an animal moves, a greater percentage of its weight is carried by the forequarter. When galloping, there is a point in the stride where the entire weight of the animal is on one foreleg. The following are the parts of the forequarter skeleton, from the top of the leg to the ground:

Scapula (skahp-yoo-lah) Also the shoulder blade or shoulder. The scapula meets with the thoracic vertebrae to form the withers. To locate the scapula, use the point of the shoulder, where the scapula and humerus join, and the middle of the withers as landmarks.

Humerus (hu-mer-uhs) The large bone in the forequarter that goes from the point of the shoulder to the elbow. The arm is the external equivalent.

Ulna and radius The ulna (uhl-nah) and radius (ra-de-uhs) are a pair of bones that form the largest long bone in the front leg. The top of the ulna creates the elbow. In some species, the ulna and radius are separate bones; in other species, the bones are fused. The external equivalent of the ulna and radius is the forearm.

Carpus (kahr-puhs) Also known as the carpal joint, this is a multi-bone joint in the front leg of an animal, located below the ulna and radius. It is commonly known as the knee in large animals. The human equivalent is the wrist.

Metacarpus (meht-a-kahr-puhs) The bones in the front leg below the carpus bones. Several metacarpal bones are in each leg, and they are numbered from the inside of the leg (medial; me-de-ehl) to the outside (lateral). In large animals, the third metacarpal bone is commonly referred to as the cannon bone.

Phalanges (fa-lahn-jez) The bones in the foot. Most species have multiple phalanges. Phalanges are numbered from closest to the body (proximal) to farthest from the body (distal), and are often coded with a P and the number. In large animals, P1 is the long pastern, P2 is the short pastern, and P3 is the coffin bone (see Figure 4-5). Phalanges are present in the forequarter and the hindquarter. Singular: phalanx.

Skeleton of the Hindquarter

The hindquarter begins at the pelvis and continues to the ground. Where the forequarter holds most of the weight, the hindquarter serves as the engine for moving the body. The hindquarter is more heavily muscled than the forequarter. In meat-producing animals, more desirable cuts of meat come from the hindquarter of the animal. In athletic animals such as horses and dogs, the skeleton of the hindquarter is of great importance in generating speed and impulsion in movement. The following are the parts of the hindquarter skeleton, from the top of the animal to the ground:


Pelvis (pehl-vihs) The pelvis (hip) is made of three pairs of bones that act as one (see Figure 4-6).During parturition, the joints holding the bones of the pelvis relax, allowing expansion of the pelvis and facilitating the delivery of the offspring. One of the external signs of impending parturition is this relaxation of the pelvis. The following are the bones that make up the pelvis:

Acetabulum (ahs-eh-tahb-yoo-luhm) The large round socket created where the three bones of the pelvis meet. The acetabulum is the "socket" of the ball and socket joint that creates the point of the hip.

Ilium (ihl-e-uhm) The largest of the bones of the pelvis, the ilium is shaped like a blade. In ruminant animals, the external part that is the ilium is known as the hook.

Ischium (ish-e-uhm) The ischium is smaller than the ilium, and forms the back of the pelvis, when viewed from the side. In ruminant animals, the external part of the anatomy that is the ischium is known as the pins.


Pubis (pew-bihs) The pubis is the smallest bone of the pelvis, and is located on the bottom of the pelvis. The pubic bones are fused in a joint known as the pubic symphysis (pehw-bihck sihm-fih-sihs).

Femur (fe-muhr) The large bone in the hind leg. The top of the femur creates a ball and socket joint, the hip; the bottom of the femur creates a hinge joint, the stifle (sti-fuhl).

Patella (pah-tehl-ah) This is the equivalent to the kneecap in humans, and is a large sesamoid bone that is located between the femur and the tibia in the hindquarter. The term knee is used in quadrupeds to refer to the carpal joint in the forequarter, and is not used to refer to the patellar joint in the hindquarter. This joint is referred to as the stifle.

Tibia (tihb-e-ah) and fibula (fihb-yoo-lah) Paired bones in the hind leg between the stifle and the hock. The tibia is large and carries the majority of the weight. The fibula is a slender bone that does minimal weight-bearing. In some species the fibula is fused to the tibia, and in others does not completely extend the length of the tibia.

Tarsus (tahr-suhs) The multi-bone joint in the hind leg below the tibia and fibula. The tarsus is also known as the hock in large animals. The tarsus is equivalent to the ankle in humans.

Metatarsus (meht-a-tahr-suhs) The bones in the hind leg below the tarsus. Just as with the metacarpus, there are several metatarsal bones, and they are numbered from the inside of the leg (medial) to the outside (lateral).

Sesamoid (sehs-ah-moyd) Small bones in both the front and hind legs. They are in the joint capsules, or embedded in tendons, in different locations. The patella is an example of a sesamoid bone, as is the navicular bone, which is in the hoof of the horse at P3.

External Anatomy

In addition to knowing the skeletal parts of the anatomy, it is important to know the common terms used to refer to the external parts of the animal that are associated with the skeletal areas. Terms for the same skeletal part often vary in different species. Knowing what terms are most appropriate for the specific species that is being discussed is also important. The following lists categorize those terms that are similar within species, as well as those that are different between species.

Avian Species

The basic external parts are the same for all avian species (see Figure 4-7). The following is a list of those parts:

Beak (bek) The hard structure that surrounds the mouth of avian species. In some companion bird species, the beak must be kept trimmed to allow the bird to eat normally. Some poultry producers trim the beaks of (debeak) chickens to prevent the chickens from injuring each other through pecking.

Comb (kom) The fleshy growth on the top of the head of a chicken. Males and females have combs, although the male comb is usually more prominent. Refer to Chapter 11 for details on different varieties of combs.

Feathers The outer covering of members of the avian species. Feathers are made of protein, and protect the body from the elements, much as hair does for mammals. The following are the many varieties of feathers:

* Contour The feathers covering the body of the bird.

* Coverts (co-verts) The feathers on the wings that start at the top of the wing and cover the bases of the primary and secondary feathers.

* Down Small soft feathers close to the body, or present on young. Down is one of the byproducts of the poultry industry, and is used in pillows, comforters, and other warm clothing.

* Hackles Long, slender feathers on the neck of some birds.

* Primary The large feathers on the ends of the wings.

* Secondary The large, stiff feathers on the portion of the wing near a bird's body.


Saddle The caudal portion of the topline of a bird. Shank The leg of the chicken between the hock and the foot.

Spurs A sharp, bony projection from the shank of some types of poultry. The bird can use the spur as part of a defense, and can cause injury to other birds or people.

Wattle (what-tuhl) Fleshy tissue located near the chin in some poultry species that dangles down below the head.


Most anatomy is the same in all four-legged animals (see Figure 4-8). Differences between species will be described in the figures. Many of the external parts are based on the location of external landmarks, which allow estimation of where the bones lie. Judging and evaluating many livestock species is a popular activity for youth and adults. A thorough understanding of the skeletal and external anatomy is vital for accurate evaluation of an animal, and clear communication of the results of that evaluation. The following are the external parts of mammals:

Cheek (chek) The muscular region on the side of the face belowthe eyes and leading forward toward the lips.

Chest (chehst) A region in the front of the animal below the neck and between the points of both shoulders.

Coffin (kawf-ihn) joint The joint between P3, the coffin bone, and P2, the short pastern bone in hooved animals.

Coronet (kor-oh-net) Also known as the coronary (kor-o-na-r-e) band, the coronet is the area where the skin of the leg meets the hoof (see Figure 4-9). Injuries to the coronary band can result in deformations of the hoof.

Crest (krehst) The top of the neck.

Croup (krewp) The region across the top of the hindquarter from the hips to the tail. Known as the rump in some species.

Dewclaw (doo-claw) A horny accessory digit on the back of the fetlock of many ruminant animals (see Figure 4-10) and pigs. In dogs and cats, dewclaws are the evolutionary remnants of toes. Some breeders choose to remove dewclaws at birth because they may become injured or damaged, especially in hunting dogs that work in fields and woods.





Dewlap Loose skin under the throat and neck of an animal. Most often used in reference to cattle and rabbits.

Dock The top portion of the tail. This term is also used for the surgical removal of all or part of the tail.

Fetlock (feht-lohk) The joint formed between the cannon bone (thirdmetacarpal) and the pastern (P1). The fetlock joint also contains two sesamoid bones.

Flank The region where the barrel meets the hind leg. Gaskin (gas-kihn) The muscular region on the inside and the outside of the tibia in the hindquarter.

Heartgirth The circumference of the area directly behind the withers and the elbows. Heartgirth measurement is related to weight, and a common way to estimate the weight of a horse is to use a weight tape to measure around the heartgirth.


Heel The back of the hoof.

Hoof (huhf) The hard foot of some animals. Animals with hooves are known as ungulates. Ungulates can have a single hoof, such as horses, or a split hoof, such as cows and pigs. Hooves are made of the same type of tissue as human fingernails, and can be trimmed with no discomfort to the animal.

Muzzle (muh-zuhl) The nose area of an animal, including the nostrils and lips.

Paralumbar fossa (pahr-ah-luhm-bahr fohs-ah) The hollow between the ribs and the hips (see Figure 4-12). Poll (pol) The area on the top of the head, between the ears.

Tailhead The part of the tail where it connects to the body.

Teat The nipple of the mammary gland. Throatlatch (throt-lach) The region of the underside of the neck where the head and neck connect. Also known as the throat or throttle.

Toe The front of the hoof in ungulates, or the individual digit in clawed animals or poultry (see Figure 4-13).

Topline The term to describe the unit created by the back, loin, and croup or rump.

Udder The mammary gland of the female of the species.

Underline The bottom of the body from the elbows to the flank.


Parts of the Hoof. The hoof supports the weight of the entire animal, and is structured to do so with minimal problems (see Figure 4-14). The following are the part of a hoof:

Bars V-shaped structure on the bottom of the hoof leading from the heel toward the toe.


Frog The arrow-shaped pad on the hoof of the horse. The frog is flexible and plays an important role in moving blood back up the leg.

Heel The back part of the hoof. The bulb of the heel is the soft tissue on the heel, and is susceptible to injury.

Hoof wall The hard outer layer of the hoof. The hoof wall primarily bears the weight of the hoof.


Laminae (lahm-ihn-nah) Structures inside the hoof.

Laminae can be sensitive (with nerves) or insensitive (without nerves). The sensitive and insensitive laminae interlock in the hoof. Inflammation of the laminae is laminitis (lahm-ihn-i-tihs), and is a serious illness in hooved animals.

Quarter The region of the hoof on the sides of the hoof between the sole and the heels.

Sole The bottom of the hoof.

White line The area of the bottom of the hoof where the sole meets the hoof wall.

Species-Specific External Anatomy Terminology

The following are terms specific to each of the following species.


Brisket (brihs-kiht) The mass of muscle and tissue covering the chest.

Hooks The protruding hip bones that are part of the pelvis closest to the head.

Pins The protruding bones of the pelvis on either side of the tail.

Switch. A tuft of hair at the end of the tail. Porcine. The following are terms specific to porcine (see Figure 4-15):

Ham The heavily muscled upper thigh.

Jowl The throat and cheek region.

Rump (ruhmp) The region of the topline that is directly above the sacral vertebrae.

Snout (snowt) The specific term for the upper lip and nose of swine.


Brisket (brihs-kiht) The mass of muscle and tissue covering the chest.

Chine (kin) The area from the withers to the loin. The thoracic vertebrae are under the chine region.

Horn butt The region between the eyes and ears where horns have previously grown.

Wattle (what-tuhl) Fleshy growths under the throatlatch of goats.


Chestnut (ches-nut) Horny tissue on the inside of the legs of horses. Chestnuts are found above the knees in the front legs, and below the hocks in the hindquarters.

Ergot (er-goht) The horny mass, similar to a dewclaw, on the back of the fetlock. The ergot is surrounded by hair.

Forelock (for-lohk) The portion of the mane that grows from the poll down the forehead of the horse.

Frog The triangular soft region of the hoof that rests between the bars on the bottom of the hoof. The frog is softer than the rest of the hoof, and assists in circulation in the leg.

Mane (man) The hair that grows from the top of the neck.

Splint bones Another term for the first and fourth metacarpal or metatarsal bones that lie on the inside and outside of the cannon bone.

Canine/Feline. The following are terms specific to canines and felines (see Figure 4-16):

Dewclaw (doo-claw) A remnant of an evolutionary toe that protrudes from the back of the metacarpals (metatarsals).

Pinna (pihn-ah) The cartilage of the ear that is external to the head.

Rump The region of the back between the hips and the tailhead.



Muscular Anatomy

The skeleton is the framework for the body, and muscles move that skeleton. Different types of muscles serve different roles, but they have some things in common. All muscles are made of groups of muscle cells called muscle fibers and expand and contract to create a specific action. Voluntary muscles are those that expand and contract in response to a conscious decision of the animal to make a movement; involuntary muscles are those that expand and contract without conscious thought (see Figure 4-17). Generally, voluntary muscles are involved in movement of the body, and involuntary muscles are involved in the functions necessary for life, such as the beating of the heart and breathing. The following is a list of the types of muscles found in animals:

Cardiac muscle (kar-de-ahck) Also known as the striated (stri-a-tehd) involuntary muscle. The striated muscle is characterized by microscopic dark bands across the muscle fiber. The cardiac muscle is involuntary, and is started by a bundle of nerves in the heart. The autonomic (aw-to-nah-mihk) nervous system, which controls involuntary muscles, can increase or decrease the heart rate, but does not initially stimulate the contraction of the muscle.


Skeletal muscle Skeletal muscles work to move the bones, and make animals ambulatory (ahm-bu-lahtor-e), or able to move. Skeletal muscles are also known as striated voluntary muscles. Skeletal muscles respond to the voluntary nervous system; a message from the nerves to contract causes a muscle to contract, and removal of the signal causes the muscle to relax. Most skeletal muscles are found in pairs, to offset each other's action. Abductor (abduchk-ter) muscles move bone away from the body, and adductor (ahd-duhck-ter) muscles move bone toward the body. Skeletal muscle makes up the majority of the meat cuts that are used by consumers.

Smooth muscle Smooth muscles are also knows as unstriated (un-stri-a-ted) involuntary muscles. These involuntary muscles are stimulated by the autonomic nervous system, which means they operate without conscious effort. Smooth muscles surround the internal organs and are not connected to the skeleton. These muscles move food through the digestive tract, and perform other basic bodily functions.

Circulatory System

The circulatory system moves blood throughout the system, carries nutrients to the cells, and brings waste products back to be released from the body. The circulatory system is made of the heart and blood vessels. The following terms refer to parts of the circulatory system:

Pulmonary (puhl-mah-na-r-e) The pulmonary circulatory system is the portion of the circulatory system that serves the lungs.

Systemic The systemic circulatory system is that which carries blood to the rest of the body.

Hepatic (heh-paht-ik) The hepatic circulatory system is a part of the systemic circulatory system, and carries blood from the internal organs to the liver, where the liver filters out waste. The filtered blood then returns to the systemic system.

Blood Vessels

Blood (bluhd) vessels Through vessels, blood transports nutrients, gasses, and waste throughout the body. Blood has the following components:

Plasma (plahz-mah) The liquid portion of blood and about 60 percent of the total blood volume. Plasma contains water, hormones, and other proteins.

Platelets (plat-lehts) The smallest components in the blood, platelets are sticky particles that converge on sites of injury. Platelets stick together to create a clot to stop bleeding.

Red blood cells Also known as erythrocytes (ehrihth-ro-si-tes), red blood cells carry oxygen and other gasses out to the body. In mammals, red blood cells do not have a nucleus; while birds do have nuclei in their red blood cells. Because mammalian red cells do not have a nucleus, they cannot generate energy, and have a short life span.

Thrombocyte (throhm-bo-si-t) Another type of cell that causes clotting at the site of a wound to stop bleeding. Platelets do not have nuclei, and thrombocytes have nuclei.

White blood cells Also known as leukocytes (looko-si-tes), white blood cells are fewer in number in the blood than red blood cells, and play an important role in the immune system. Neutrophils (nu-tro-fihls), eosinophils (e-o-sihn-o-fihls), basophils (ba-so-fihls), monocytes (mohn-o-sits), and lymphocytes (lihm-fo-sits) are all types of white blood cells.

Arteries (ahr-ter-ez) Arteries carry blood away from the heart. Arteries have three layers, an outer layer of connective tissue, a middle layer of smooth muscle tissue, and an inner layer of endothelial (en-do-the-le-ehl) tissue. The artery is flexible enough to absorb some of the pressure of the pumping of blood. The pulse of the heart pumping can be felt in arteries near the skin surface. The following are types of arteries:

Aorta (a-or-tah) The largest artery, the aorta leads from the heart and branches into smaller arteries to carry blood throughout the body.

Arterioles (ahr-te-r-e-olz) The smallest of arteries, arterioles are almost completely smooth muscle cell.

Pulmonary Carries blood from the heart to the lungs. The pulmonary artery has two branches, one to each lung.

Capillaries (kahp-ih-lar-ez) Capillaries are the smallest of the blood vessels, and the walls are made up of cells that allow oxygen, nutrients, and waste products to be exchanged between the capillaries and the cells. Capillaries transition between the arterial system and the venous (ve-nuhs) system.

Vein (ven) Veins carry blood from the cells back to the heart and lungs. Whereas arteries carry nutrients and oxygen to the cells, veins carry waste products, such as carbon dioxide and water, back through the system for disposal. Veins are much less muscular than arteries, and have valves that stop the blood from flowing back in the veins. The following are types of veins:

Pulmonary Two veins from each lung that carry oxygenated blood back to the heart for circulation throughout the rest of the body.

Vena cava (ve-neh ca-veh) The large veins leading into the heart. The anterior or cranial vena cava carries blood from the head and upper body, and the posterior or caudal vena cava carries blood from the lower or hind part of the body.

Venules (ven-yuhlz) Small veins that lead from the capillaries to the larger veins.


The heart powers the circulatory system. The rhythmic pumping of the heart pushes blood through blood vessels throughout the body (see Figure 4-19). The following are parts of the heart:

Atrium (a-tre-uhm) The atria (a-tre-ah) are two of the four chambers of the heart. Veins bring blood from the body into the atria. Blood enters the right atrium from throughout the body, and blood enters the left atrium from the lungs.

Coronary blood vessels (kor-oh-nar-e) The blood vessels that serve the heart. Although blood from throughout the body travels through the heart, the coronary veins and arteries provide the nutrients and remove the waste from the heart muscle.

Ventricles (vehn-trih-kuhlz) The ventricles do the pumping, and are more heavily muscled than the atria. Blood moves from the right atrium to the right ventricle. The right ventricle pumps blood to the lungs. The blood then comes from the lungs through the left atrium to the left ventricle. The left ventricle then pumps blood throughout the body.

Digestive System

The digestive (di-jehs-tev) system takes feedstuffs and breaks them down so that the body can use the nutrients and energy from the food. Details on that process will be covered in Chapter 5 on nutrition. In this section, we will focus on the organs that make up the digestive system, which is also known as the gastrointestinal (gahs-tro-ihn-tehst-i-nehl) tract (see Figure 4-20). Digestive tracts have evolved differently for different species, depending on their primary food source. The following are components of the digestive system in the order in which food would pass through the system:



Mouth The mouth is the entrance to the digestive tract and contains many of the structures that begin the mechanical and chemical process of breaking down food.

Tongue (tuhng) The muscular organ in the mouth that moves food during chewing, and has the taste buds, or papillae (pah-pihl-a), that taste the food.

Teeth The teeth begin the mechanical breakdown of food. Different species have different combinations of teeth types, which are divided into the following four primary types with different functions (see Figure 4-21).

Incisors (ihn-siz-or) The front teeth that cut through food.


Canines (ka--no-n) The pointed teeth next to the incisors. Canines, or fangs, are more pronounced in predatory animals, and are used for grasping food.

Premolars (pre-mo-lahr) The teeth immediately preceding the molars. Premolars are also sometimes called bicuspids (bi-cuhs-pid) because they have two points on the surface.

Molars (mo-lahr) The large flat surfaced teeth in the back of the jaw that do most of the grinding of food.

Salivary glands (sahl-ih-vahr-e- glahndz) The glands around the mouth that secrete saliva (sah-li-vah), which introduces moisture and digestive enzymes to the food.

Esophagus (e-sohf-ah-guhs) The tube that carries food from the mouth to the stomach. The esophagus is a muscular tube that ends in a muscular ring, the sphincter (sfingk-ter), at the stomach.

Stomach The stomach is a muscular organ that is the site of the majority of digestion. The stomach adds digestive chemicals to the food, and muscular contractions of the stomach assist in mechanical breakdown of food. Stomachs are divided into two types, monogastric (mon-no-gahs-trihck) and ruminant (roo-mihn-ehnt).

Monogastric The monogastric has a single stomach. Examples of monogastric animals are humans, dogs, cats, and pigs. In monogastric digestive systems, the majority of digestion occurs in the stomach. In the stomach, gastric juices (which are very acidic) are introduced to the food and break it down to prepare it for absorption. Feedstuffs are broken down into a liquid called chyme (kim), which is then moved into the small intestine.


Ruminant The ruminant stomach has multiple compartments (see Figure 4-22).Examples of ruminant animals are cattle, sheep, goats, and llamas. The llama is a modified ruminant, and has three stomach compartments, instead of the four found in other ruminants. The following are the four compartments of the ruminant digestive system:


Rumen (roo-mehn) The largest portion of the stomach of ruminant animals. The rumen is the site of fermentation of the foodstuff after ingestion. When animals have consumed enough food to fill the rumen, they lie down and ruminate (roo-mih-nat), which is the regurgitation of foodstuff up the esophagus for further chewing.

Reticulum (re-tihck-yoo-luhm) The portion of the stomach that contains a series of membranes that create a honeycomb-like effect. After initial consumption of food, the solid portions stay in the rumen, and the liquid portions move to the reticulum.

Omasum (o-ma-suhm) The muscular portion of the stomach that does some grinding, and squeezes water out of the food bolus.

Abomasum (ahb-o-ma-suhm) The "true" stomach. Activity in the abomasums of the ruminant is similar to the stomach in the nonruminant.

Small intestine After initial digestion in the stomach, digestion continues in the small intestine. The small intestine is the site of the absorption of most nutrients. The small intestine includes the following three sections:

Duodenum (doo-wahd-nuhm or doo-o-de-nuhm) The segment of the small intestine nearest the stomach.

Jejunum (ja-joo-nuhm) The middle segment of the small intestine.

Ileum (ihl-e-uhm) The last segment of the small intestine.

Cecum (se-kuhm) The cecum is located where the small intestine meets the large intestine. In most species, the cecum does not have a major role in digestion; however, in horses, the cecum is a major site of digestion and fermentation of high-fiber feed. Large intestine The majority of nutrients are absorbed in the small intestine, and the large intestine absorbs water from what remains of the feedstuff (see Figure 4-23). The following are the parts of the large intestine:

Colon The part of the large intestine from the cecum to the rectum.

Rectum (rehck-tuhm) The end of the large intestine. Anus (a-nuhs) The terminal end of the digestive tract. Feedstuffs that are left after digestion are excreted through the anus as feces (fe-sez).

In addition to the digestive tract, which runs as a continuous tube through the body, the following organs play important roles in digestion and utilization of feedstuffs:

Liver (liv-ehr) One of the largest glands in the body, the liver produces bile (bi-l), which helps break down fat in foods. The gall bladder (gahl blahd-der) is located in the liver, and stores bile in all animals except horses and rats, which continually excrete bile into the small intestine, instead of storing it in the gall bladder.

Pancreas (pahn-kre-uhs) The pancreas produces the digestive enzymes trypsin (trihp-sihn), lipase (li-pas), and amylase (ahm-ih-las). The pancreas also produces the hormone insulin (ihn-suhl-ihn).

Avian Digestive System

The avian digestive system has some specific differences when compared to a mammalian digestive system (see Figure 4-24). The mouth in avian species does not contain teeth, and is simply used to pick up and swallow food. The esophagus leads to the crop, which stores the feed and adds saliva for moisture. From the crop, food moves through the proventriculus (pro-ven-trick-yoo-luhs), the glandular stomach, to the muscular stomach, also known as the gizzard (giz-erd). The muscular gizzard contracts to grind the feed into smaller pieces before it moves to the small intestine for nutrient absorption, the large intestine for absorption of water, and then remaining material is excreted through the cloaca (klo-a-kah) and vent (vehnt). Avian species have ceca (se-kah), the plural of cecum, but the exact function of the ceca is unclear.

Reproductive System

The reproductive (re-pro-duhck-tihv) system provides for the production of the next generation of offspring. The study and science of reproduction is also known as theriogenology (ther-e-o-jehn-ohl-oj-e). Reproductive organs are called genitals (jehn-ihtahlz), and differ in males and females. In addition to producing gametes (gahm-ets), which are the cells containing the genetic material from each parent, the genitals produce many of the chemicals called hormones (hor-monz), which are involved in controlling the reproductive process.

[FIGURE 4-24]

[FIGURE 4-25]

Male Reproductive System

Male reproductive systems vary in appearance between species, but many of the anatomical parts serve similar purposes (see Figure 4-25). The following are parts of the male reproductive system:

Accessory glands Glands such as the prostate (prohstat), bulbourethral (buhl-bo-yoo-re-thrahl), and vesicular (vehs-ih-koo-lar) glands that produce fluids to nourish and protect sperm. Fluids produced by the accessory glands also flush urine from the urethra. There is some variation across species regarding accessory glands. Swine have an ampulla (ahmp-yoo-lah), and in horses, the vesicular glands are known as seminal vesicles (sehm-ih-nahl vehsihkuhlz).

Acrosome (ahk-ro-zom) A structure on the sperm cell containing enzymes that allow the sperm to penetrate the ovum for fertilization.

Cloaca (klo-a-kah) An external reproductive organ in male and female birds. In males, the cloaca holds sperm cells until the rudimentary penis transfers them to the female cloaca.

Epididymis (ehp-ih-dihd-ih-mihs) A tube on the testicle that stores semen prior to ejaculation.

Leydig's cells (lih-dihgz sellz) Cells that produce hormones such as testosterone.

Penis (pe-nihs) The male sex organ that delivers sperm into the female reproductive tract. The penis also serves as the organ to facilitate excretion of urine from the body.


Scrotum (skro-tuhm) The skin sac that encloses and supports the testes outside the male body (see Figure 4-26). The testicles of mammals must be cooler than the body temperature to allow production of live sperm.

Sigmoidflexure (sihg-moyd flehck-sher) An S-shaped bend in the penis of boars and bulls.

Sperm (sperm) Male sex cells (see Figure 4-27). The sperm carry the DNA that the male will contribute to the offspring. The sperm cell is divided into three major parts: the head, which contains the genetic information; the body, which connects the head to the tail; and the tail, which allows the sperm cell to swim.

Spermatazoa (sper-mah-to-zo-ah) Another term for male sex cells. Singular form spermatozoon (spermahto-zo-uhn).

Testes (tehs-tez) Glands that produce spermatozoa and male sex hormones. Singular form testis (tehstihs).

Testicles (tehs-tih-kuhlz) Another term for testes.

Urethra (yoo-re-thrah) A tube that runs through the penis that carries urine from the urinary bladder, or semen from the testicles.

Vas deferens (vaz dehf-er-ehnz) A tube that carries sperm from the epididymis through the penis.

Female Anatomy and Physiology

As in the male, the appearance of some aspects of the reproductive tract may have differences, but the functions are very similar (see Figure 4-28). The following are terms related to female anatomy:

Albumen (al-bu-men) The protein-rich white of the egg. It is added to the yolk after ovulation when the yolk travels through the magnum portion of the oviduct.


Cervix (sihr-vihckz) The cervix separates the uterus from the more external reproductive organs. The cervix relaxes during estrus to allow the sperm to enter the reproductive tract. It then closes until the next estrus, or until it is time to deliver an offspring.

Corpus luteum (kor-puhs loo-te-uhm) Cells formed from the follicular cells after ovulation. The corpus luteum is yellow, and produces progesterone. Each ovulated follicle produces a corpus luteum, so animals that ovulate several follicles will have several corpora lutea (kor-per-ah loo-te-ah).


Fallopian tube (fah-lo-pe-ahn) Another term for oviduct. Oviduct is the preferred term in a professional atmosphere.

Follicle (fohl-lihck-kuhl) The sac on the ovary that contains the ova. As the follicle matures, it produces estrogen and enlarges until it ovulates and releases the ova. The following are types of follicles:

* Primordial Immature follicles in the ovary.

* Secondary Follicles that have begun to mature and produce estrogen.

* Graafian (grahf-e-ahn fohl-lihck-kuhlz) Fully mature follicles that either ovulate or go through atresia, which means they stop development and are reabsorbed by the ovary.

Germ cell In avian species, the portion of the yolk that contains the genetic information.

Infundibulum (ihn-fuhn-dihb-yoo-luhm) An opening at the end of the oviduct near the ovary. The infundibulum, and the fimbriae (fihm-bre-ah) at the ends of the infundibulum, act as a "catcher's mitt" and catch the ova when they leave the ovary. The infundibulum and fimbriae are not connected to the ovary. In avian species, sperm are stored in the infundibulum until the egg (yolk) arrives for fertilization.

Mammary glands (mahm-mah-re) Mammary glands are present in all mammals, and produce milk for the young (see Figure 4-29). The number of glands present varies with species. The following are components of mammary glands:


Alveoli (ahl-ve-o-li) The milk-producing part of the mammary gland. The saclike alveoli are arranged in lobes and lobules in the mammary gland.

Cisterns Areas of the mammary gland that store milk. The teat cistern is located in the teat, and the udder cistern is located in the udder.

Sphincter muscle A muscle that closes the streak canal.

Streak canal The opening from the teat cistern, through the teat, that milk travels through to leave the mammary gland.

Teat (tet) The external portion of mammary gland that delivers milk to offspring.

Oocyte (o-o-sit) An egg cell.

Ova (o-vah) Egg cells. Singular form ovum (o-vuhm).

Ovary (o-vah-re) The female gonad that produces ova as well as numerous female reproductive hormones. Mammalian species have two active ovaries, whereas avian species have one functional ovary.

Oviducts (o-vih-duhckts) Tubes that lead from the ovary to the uterus. Oviducts are not connected to the ovary. Oocytes travel through the oviduct, and in most species, fertilization occurs in the oviduct. The following are parts of oviducts that are important in avian reproduction:

* Magnum (mayg-nuhm) In birds, this is the part of the oviduct where the albumen is secreted to surround the yolk.

* Isthmus (ihs-muhs) The part of the oviduct where shell membranes are added.

Placenta (plah-sehn-tah) The organ that joins the fetal unit with the uterus. The placenta exchanges nutrients and waste products between the fetus and the mother, and is expelled at parturition.

Sperm nests In birds, sperm nests are locations in the oviduct where sperm can survive for several weeks. Eggs are fertilized when they pass over the sperm nests. Longevity of sperm varies by individual rooster and by species.

Urethra (yoo-re-thrah) The tube running from the bladder to the floor of the vagina that carries urine out of the body.

Uterus (yoo-ter-uhs) The muscular organ of the female. In mammals, this organ is the location for the development of the offspring. In avian species, this organ is where the shell is added to the egg. The uterus has the following three primary tissue layers:

* Perimetrium (pehr-ih-me-tre-uhm) The outer uterine layer.

* Myometrium (mi-o-me-tre-uhm) The middle, muscular layer that contracts to deliver the fetus.

* Endometrium (ehn-do-me-tre-uhm) The inner layer that is primarily responsible for supporting the fetus.

Uterine body The portion of the uterus that is furthest from the oviduct. The cervix marks the end of the uterine body.

Uterine horn (yoo-ter-ehn) The portion of the uterus between the uterine body and the oviduct. Some species have bicornuate (bi-korn-yoo-at) uteruses, which have large, well-defined uterine horns. In other species, the uterine body is the dominant structure and the uterine horns are quite small.

Vagina (vah-ji-nah) The structure that leads from the internal reproductive tract out of the body. The vagina receives the penis during copulation and serves as the "birth canal" during parturition.

Vulva (vuhl-vah) The external reproductive organ in females. Is some species, physiological changes of the vulva occur when they are in estrus, assisting in detection of estrus.

Endocrine System

Many of the processes in the body are controlled by hormones (ho-r-mo-nz), which are chemicals manufactured and released in the body in one set of cells, but that have an action on another set of cells. The study of these hormones, and how they work is called endocrinology (endo-cre-nahl-ahge). The same basic hormones control processes in all mammalian species, although species differ in timing and release patterns of the hormones. These differences are especially apparent in the control of the reproductive process (see Figure 4-30).


Endocrine Organs and Hormones They Produce

Most functions of the body are controlled by hormones. The following list identifies the important endocrine organs, and identifies the primary hormones produced by each of those organs:

Pineal gland (pi--ne-ahl) The pineal gland is located in the brain, and responds to changes in day length. The primary hormone produced by the pineal gland is melatonin (mehl-ah-ton-ihn), which controls the timing of the reproductive season.

Hypothalamus (hi-po-thahl-ah-muhs) Located at the base of the brain, the hypothalamus releases gonadatropin-releasing hormone (GnRH) (ge-nad-ah-tro-pen), which stimulates the anterior pituitary gland to produce follicle-stimulating hormones and luteinizing hormones.

Pituitary gland (pih-too-ih-tar-e) The "master gland," the pituitary is divided into anterior and posterior sections and the hormones released from the pituitary gland have many roles (see Figure 4-31). Anterior pituitary glands produce hormones that then act on target organs elsewhere in the body. The anterior pituitary controls many of the functions of the body. The following hormones are all produced by the anterior pituitary gland, and then travel to other organs to elicit another response:

Adrenocorticotropic hormone (ACTH) (ahd-re-no-kor-tih-ko-tro-pihck) Acts on the adrenal glands to stimulate the release of cortisol and other glucocorticoids.

Follicle-stimulating hormone (FSH) A hormone released from the pituitary gland that stimulates the follicles to develop in the female, and stimulates sperm production in the male.

Growth hormone (GH) Stimulates growth of tissues in the body. Also known as somatotropin. Luteinizing hormone (LH) (loo-ten-iz-ing) A

hormone released from the anterior pituitary gland that has several roles in reproduction. LH stimulates ovulation. After ovulation occurs, LH acts on the ruptured follicle to create the corpus luteum. In males, LH stimulates the Leydig's cells to produce testosterone.

Prolactin (pro-lahck-tihn) Stimulates milk production.

Thyroid-stimulating hormone (TSH) Acts on the thyroid to stimulate production of thyroid hormones.

Posterior pituitary gland Secretes hormones that act directly on the target organs, whereas most of the hormones secreted from the anterior pituitary are "stimulating hormones." The following are hormones secreted by the posterior pituitary gland:


Antidiuretic hormone (ADH) (ahn-tih-di-yoo-rehtihck) Also known as vasopressin, antidiuretic hormone controls the volume of water in the circulatory system through the kidneys.

Oxytocin (ahk-se-to-sen) Stimulates smooth muscle contraction in the mammary gland and the uterus, resulting in milk moving downward through the mammary gland (milk letdown) and uterine contractions.

Thyroid (thi-royd) A gland located in the neck, near the larynx. Triiodothyronine (T3) (tri-i-o-do-tho-ro-nen) and thyroxine (T4) (thi--rohcks-ihn) regulatemetabolism. Calcitonin (kahl-sih-to--nihn) controls absorption of calcium.

Pancreas (pahn-kre-ahs) The pancreas secretes insulin (ihn-suh-lihn) and glucagon (gloo-kah-gohn), which are produced in specialized cells called the Islets of Langerhans (i-lehts ohf lahng-er-hahnz). Insulin lowers blood glucose by moving glucose into cells, and glucagon increases blood glucose by moving glucose out of cells into the blood.

Gonads In addition to production of gametes, gonads play an important endocrine role in the production of hormones. The following list indicates which hormones are produced by which gonads:


Testosterone (tehs-tahs-ter-on) The primary male reproductive hormone. Testosterone is produced by the Leydig's cells in the testes, and controls reproductive behavior and development of secondary sex characteristics in males.


Estrogen (ehs-tre-gen) The dominant female reproductive hormone, estrogen is produced by the follicles on the ovary, controls reproductive behavior and development of secondary female characteristics, and acts upon the uterus to prepare it for the arrival of a zygote.

Progesterone (pro-jehs-te-ron) The female primary hormone during pregnancy. Progesterone is produced by corpora lutea and maintains pregnancy in the female.

Adrenal glands Located near the kidneys, the adrenal glands produce hormones in the adrenal cortex or in the adrenal medulla. The adrenal cortex is the outer layer of the adrenal gland, and produces glucocorticoids (gloo-ko-kor-tih-koydz) and mineralocorticoids (mihn-er-ahl-o-kor-tih-koydz). Glucocorticoids control metabolism of fats, proteins, and carbohydrates, and have anti-inflammatory capabilities. Mineralocorticoids control water and mineral balance in the body. The adrenal medulla is the center of the adrenal gland and produces epinephrine (ehp-ih-nehf-rihn) and norepinephrine (nor-ehp-ih-nehf-rihn). Epinephrine and norepinephrine are released in response to stress, and increase the heart rate, blood pressure, and the amount of blood glucose available for the muscles.

Prostaglandin (prahs-tah-glan-den) A broad category of hormones that are produced in various cell types. The most important one in animal science is prostaglandin F2-alpha, a hormone which breaks down the corpora lutea, which results in the halting of progesterone production, and the progression of the female through the estrous cycle. Prostaglandin can be produced in a wide variety of cell and tissue types, and is often used to manipulate the estrous cycle in mammals.


Respiratory System

The respiratory (rehs-pih-rah-tor-e) system brings oxygen into the body and removes carbon dioxide from the body (see Figure 4-32). Respiration (rehs-per-a-shuhn) is the exchange of gasses, and can occur either in the cells (internal or cellular respiration) or in the lungs (external respiration). In mammals, the lungs are the primary organs of the respiratory system. The diaphragm (di-eh-frahm) is a large muscle below the lungs. Contraction and relaxation of the diaphragm expands and contracts the chest cavity to pull air in and force air out of the lungs.

Mammalian Respiratory System

The following are components of the respiratory system of mammals:

Nostrils (nahs-trihls) The first part of the respiratory system is the nostrils. The nostrils are used to draw air into the respiratory system. Some animals can also inhale air through their mouths.

Nasal cavity (na-zehl) The cavity just inside the nostrils. Air is warmed and moisture is added in the nasal cavity. This is also where particles of dust are removed, and the olfactory receptors (ohl-fahck-tor-e re-sep-torz) detect smells.

Pharynx (far-ihnks) The area in the back of the throat where the respiratory and digestive systems meet. In animals that breath through both the nose and mouth, air from both sources meets in the pharynx. The epiglottis (ehp-ih-gloht-his), which prevents food from entering the lungs, is located in the pharynx.

Larynx (lar-ihnks) The cartilage structure in the throat that contains the voice box and the vocal cords.

Trachea (trak-e-ah) The trachea is also called the windpipe, and carries air to the bronchi. The trachea is made of rings of cartilage that help it maintain its shape. The trachea divides into two branches called bronchi (brohng-ki) in the chest cavity.

Bronchioles (brohng-ke-ohlz) Bronchi continue to branch in the lungs. The smaller branches of bronchi are bronchioles (see Figure 4-33).

Alveoli (ahl-ve-o-li) The terminal ends of the bronchioles. Alveoli have extremely thin walls and interface directly with capillaries. The actual exchange of gasses occurs in the alveoli. Singular: alveoulus (ahl-ve-o-luhs).



Avian Respiratory System

There are some significant differences between the avian and the mammalian respiratory systems (see Figure 4-34). Avian species have a nasal chamber that opens into the mouth, where the air then travels to the trachea. Instead of the pharynx and larynx that exist in mammals, birds have a syrinx (sehr-ihncks) at the end of the trachea that produces sound. Birds also have air sacs at the ends of the bronchi and into the bones. Gas exchange occurs through air capillaries, instead of through alveoli. Contraction and relaxation of muscles in the chest and abdomen create breathing. Birds do not have a diaphragm.

Urinary System

The urinary system removes liquid waste from the body. Many of the parts of the urinary system are shared with the reproductive system (see Figure 4-35). The kidney is the primary organ of the urinary system, and filters waste products from the blood. In addition to filtering waste out of the system, the kidney plays an important role in maintaining proper hydration in the body. The kidneys remove excess water when it is present, and conserve water when it is scarce. The following are the parts of the kidney and urinary system:

Nephron (nehf-rohn) The part of the kidney that filters the blood. The glomeruli (glo-mer-yoo-li) are the capillaries that are part of the nephron.

Ureters (yoo-re-terz) The paired tubes that carry urine from the kidney to the urinary bladder. Urinary bladder The organ where urine is stored until it is excreted from the system.

Urethra (yoo-re-thrah) The tube that carries urine from the urinary bladder outside the body. In males, the urethra also carries semen.


Match the correct skeletal part with the correct external part.
Skeletal Part External part

1. -- Humerus             a. Stifle

2. -- Cranium             b. Coffin bone

3. -- P3                  c. Croup

4. -- Third metacarpal    d. Arm

5. -- Thoracic vertebra   e. Hock

6. -- Carpal joint        f. Skull

7. -- Tarsal joint        g. Cannon bone

8. -- Patellar joint      h. Back

9. -- Sacral vertebrae    i. Knee

10. Where in the digestive tract does the most absorption of nutrients
take place?

a. Stomach

b. Small intestine

c. Large intestine

d. Cecum

11. Describe the structural differences between a vein and an artery.

12. What four parts make up the ruminant stomach, and what is the role of each part?

13. List the three muscle types, and give an example of where in the body each muscle type is found.

14. List the types of connective tissue, and give an example of where each type of connective tissue would be found.

15. What are the parts of the pulmonary circulatory system?

16. What types of feathers are found on the wings of birds?

17. Properly label the parts of the heart indicated in Figure 4-36.

18. Label the parts of the sperm cell, and identify the primary role of each part.

19. List the parts of the female mammalian reproductive tract in order, from the ovary to the vulva.

20. List the bones in the front leg of the cow in order from the ground to the top.

21. Name two parts of the avian female reproductive tract that are not found in the mammalian reproductive tract.

22. What is the purpose of "sperm nests" and in what species do they exist?


The number of vertebrae in common domestic species

Species         Cervical   Thoracic   Lumbar    Sacral    Coccygeal

Avian            14         7                  Fused-14     6
Bovine           7          13         6          5         18-20
Canine/Feline    7          13         7          3         6-23
Caprine          7          13         6-7        4         16-18
Equine           7          18         6 *        5         15-21
Ovine            7          13         6-7        4         16-18
Porcine          7          14-15      6-7        4         20-23

* Some Arabians have five lumbar vertebrae.
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Author:Brady, Colleen
Publication:An Illustrated Guide to Animal Science Terminology
Geographic Code:1USA
Date:Jan 1, 2008
Previous Article:Chapter 3 Animal genetics and breeding.
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