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Morphometric evaluation of foramen magnum for sex determination in a documented north Indian sample.

INTRODUCTION: The occipital bone is frequently used in forensic anthropology that seeks to determine the sex. Indexes have been built from the dimensions of the foramen magnum, and various authors have reported its usefulness in determining the sex, (6-9) indicated that the sagittal and transverse dimensions of the foramen magnum were significantly higher in men's skulls. In another study, (10) examined the usefulness of determining the dimensions of the foramen magnum in the diagnosis of sex.

The occipital bone being described as perforated by the foramen magnum which is a unique and complex anatomical region within the basal central region of the occipital bone. The anterior border of the foramen magnum is formed by basilar process of the occipital bone, the lateral border by the left and right ex-occipitalis and posterior border is formed by the supra-occipital.

Due to the thickness of the cranial base and its relatively protected anatomical position, this area of the skull tends to withstand both physical insults and inhumation somewhat more successful than many other areas of the cranium (11).

Most of the previous studies of sex differences in the skull were centered on morphological traits in a descriptive manner (cranioscopy). (12-19).

Although, there are numerous methods of measurement used in biological anthropology, but 'anthropometry' is unique in its contribution and peculiarity (20). Anthropometry is a series of systematized measuring techniques that express quantitatively the dimensions of the human body and skeleton. Anthropometry is often viewed as a traditional and perhaps the best tool of anthropology. It is highly objective and reliable in the hands of trained anthropometrist. The metric approach is more objective and less dependent on observer experience. Its replicability is high and it is more amenable to statistical analysis. However, it depends on identifiable and unambiguous osteometric landmarks (21).

(1) Examined sex determination of the skull by discriminant function analysis using ((22) technique. (23) Claimed up to 100% accuracy in predicting sex from foramen magnum region. There has been no previous documented evaluation of the foramen magnum region within the area under study.

The primary goal of this research is to document and analyze the foramen magnum of this region and to investigate its reliability in sex prediction.

MATERIAL AND METHODS: This study was conducted on 68 human adult skulls (38 male and 30

females) of known sex and age (22 to 60 yrs), having no skull anomaly collected from museum of anatomy department of TMMC & RC Moradabad and also from nearby medical colleges of same geographical, cultural and climatic conditions. Sexing of the skull was done as per (24) (see- table-1).

Following measurements of foramen magnum were taken for the study:

1. Anteroposterior diameter of foramen magnum--maximum internal length of the foramen magnum along the midsagittal plane, from opisthion to basion (25).

2. Transverse diameter of foramen magnum--maximum internal width of the foramen magnum along the transverse plane.

Other researchers have used image analysis techniques in such as (5) analyzing the sagittal and transverse diameters and the area of the foramen magnum in computerized tomographic images.

Statistical analysis was done using t-test, and a value of p<0.05 was considered significant.

RESULTS: The dimensions of the foramen magnum were significantly higher in men's skulls (table-2.1) & (table 2.2)

DISCUSSION: The sex discriminant value of the foramen magnum has attracted attention of (26) (9) (27) (1) & (2). In the sample analyzed, a significant sexual dimorphism in the foramen magnum dimensions was observed. Metrically the indexes have been built from the dimensions of the foramen magnum and various authors have reported its usefulness in determining the sex. (6-8). Sexual dimorphism using Foramen Magnum have been established by direct metric measurements on the skull (28-30) and also by using computed tomographic images on skull as well as living individuals (31) & (32). (31) Found all dimensions were larger in males than females. (See table-2.3 & 2.4).

The comparison of the morphometric analysis obtained in this study with the results of other studies showed that the anteroposterior diameter of the foramen magnum (male) in the present study is (36.9 [+ or -] 0.2) Similar to anteroposterior diameter of foramen magnum of female skulls of present study (32.9 [+ or -] 0.3). Regarding the transverse diameter of the foramen magnum, in present study male skulls (31.5 [+ or -] 0.27) the same measure for the female skulls of the present study (29.5 [+ or -] 0.28). Our study well correlates with the study of (31) One very interesting fact can be observed that all values of female are lower than male values, which shows that these parameters are very important for sex determination and constitution of biological profile.

The width of the foramen magnum of Brazilian skulls showed significant results with the predominance of males over females. According to (33) this difference is related to the fact that the main neurovascular bundle such as the cervical spinal cord, vertebral arteries before and after, nerves and meninges pass through the skull base. Thus, the area of foramen magnum is larger in males due to larger structure of skeletal muscle in men.

In another study, (34) found the dimensions of foramen magnum in Indian sample to be sexually dimorphic and reported up to 100% accuracy of correctly identifying sex using simple demarking points.

The accuracy in the classification is lower than those reported for majority of sexual dimorphism morphological indicators for the occipital bone, and hence, the indexes and tables of the expected range of foramen magnum dimensions in skulls of men and women should be used only as a first approximation to the diagnosis of sex, which is more accurate when we look at the qualitative features of the occipital bone, such as the roughness of the nuchal lines, the shape of the occipital condyles, and the characteristics of the external occipital protuberance.

Values are specific for a particular population, and become low when applied to populations with a large ethnic mix, this also happens in other indicators (35-37).

A review of literature reveals scanty information in sexual dimorphism based on foramen magnum in Indian populations. Therefore, present study has been undertaken with a view to augment data in this direction and to assess the level of sexual dimorphism present in the basal region of the occipital bone in a documented Indian sample.

ACKNOWLEDGEMENT: Authors wish to acknowledge the previous researchers in this field who gave us an idea for evaluating base line values in northern India and its role in sexual dimorphism.


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S.K. Jain [1], Alok Kumar Choudhary [2], Pankaj Mishra [3]


[1.] Professor, Department of Anatomy, TMMC & RC, TMU, Moradabad, U.P.

[2.] Assistant Professor, Department of Anatomy, SGRRIMHS, D. Dun.

[3.] Professor, Department of Statistics, SGRRIMHS, D. Dun.


Dr. S.K. Jain, Professor, Department of Anatomy, TMMC & RC, TMU, Moradabad, U.P.

Date of Submission: 07/10/2013.

Date of Peer Review: 08/10/2013.

Date of Acceptance: 15/10/2013.

Date of Publishing: 17/10/2013
Table: 1

S.N      Traits              Male                   Female

1     General size   Large                   Small
2     Architecture   Rugged                  Smooth
3     Supraorbital   Medium to large         Small to medium
4     Mastoid        Medium to large         Small to medium
5     Occipital      Muscle lines and        Muscle lines and
        area           protuberance            protuberance
                       marked                  marked not marked
6     Frontal        Small                   Large
7     Parietal       Small                   Large
8     Orbits         Squared, lower,         With rounded,
                       relatively smaller      higher, relatively
                                               larger, with sharp
9     Forehead       Steeper, less rounded   Rounded, full,
10    Cheek bones    Heavier, more           Lighter, more
                       laterally arched        compressed
11    Mandible       Larger, higher          Small with less
                       symphysis, broader      corpal and ramus
                       ascending ramus         dimensions
12    Palate         Larger, broader,        Small and tends to
                       tends to U-shape        parabola
13    Occipital      Large                   Small
14    Teeth          Large, lower M1 more    Small, more often
                       often 5 cusped          4 cusp


S.N.           Parameter           Max         SD

1      Transverse diameter         31.5   [+ or -] 0.27
2      Antero posterior diameter   36.9   [+ or -] 0.2


S.N.           Parameter           Max         SD

1      Transverse diameter         29.5   [+ or -] 0.28
2      Antero posterior diameter   32.9   [+ or -] 0.3


S.N.              Parameter           Max         SD
M = 144

1         Transverse diameter         30.6   [+ or -] 2.5
2         Antero posterior diameter   36.5   [+ or -] 0.2


S.N.   Parameter                   Max    SD

1      Transverse diameter         29.5   [+ or -] 1.9
2      Antero posterior diameter   35.6   [+ or -] 2.5
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Author:Jain, S.K.; Choudhary, Alok Kumar; Mishra, Pankaj
Publication:Journal of Evolution of Medical and Dental Sciences
Article Type:Report
Geographic Code:9INDI
Date:Oct 21, 2013
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