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Journal of the Anatomical Society of India

Sexing of Skull by New Metrical Parameters in Western India

Author(s): Chimmalgi M, Kulkarni Y, Sant SM

Vol. 56, No. 1 (2007-01 - 2007-06)

Chimmalgi M, Kulkarni Y, Sant SM

B J Medical College, Pune, India

Abstract:

Sexing of the skull has great implication in medico-legal cases. In our study, we have tried to evaluate some of the tested metrical parameters in sexing the skulls of western Indian origin. In addition, the quest for new, reliable and effective metrical parameters led us to evaluate the efficacy of areas of ‘foramen ovale’ and the ‘carotid canal opening’ on the base of the skull in determining the sex. This study was conducted on 85 adult skulls of known sex (43 male and 42 female). Measurements were taken using vernier calipers and spreading calipers.

Statistical analysis showed significance between sexes for all the parameters. For each parameter identification point, demarking point and the limiting point (cut-off point) were determined. The limiting points used to sex the skulls were 122 mm for bizygomatic diameter, 31 mm2 for combined area of foramen ovale and 47.5 mm2 for combined area of carotid canal. Of these parameters, combined area of carotid canal opening showed least error with 85% accuracy for male skulls and 90% accuracy for female skulls. When combination of two parameters was considered, error dropped to 0-7%, but no added advantage was noted in combining more than two parameters. The combination of bizygomatic diameter and combined area of carotid canal was found to be best in determining the sex of skulls with 100 % accuracy.

KEY WORDS: Stylohyoid, stylochondrohyoideus, styloid process, hyoid arch.

INTRODUCTION

In medico-legal cases, bones form important evidence in establishing identity of the deceased. They provide clues regarding race, age, stature and sex of an individual. Sex of an individual can be identified accurately in 90% of the cases using pelvis alone, 80% of cases using skull alone and in 98% cases using pelvis and skull together.

Sexing of the skull is predominantly done using nonmetrical parameters, which are at best appropriate only in relative terms. The known metrical parameters fail to show clear differences between the sexes. Hence a need was felt to establish more effective new metrical parameters. Along with old parameters, two new parameters are used in the present study, namely, (a) combined area of foramen ovale and (b) combined area of carotid canal opening on the basal aspect.

Objectives of the present study were to -

  • Determine the efficiency of areas of foramen ovale and carotid canal as new parameters to determine the sex of an individual
  • Compare the efficiency of uni-variant with multivariants.

Materials and Methods

This study was conducted on 85 adult skulls of known sex (43 male and 42 female) collected from Govt. Medical College, Aurangabad and B J Medical College, Pune. With the help of Vernier calipers, spreading calipers and steel probe following measurements were taken:

  1. Maximum length of the skull measured from nasion to inion.
  2. Maximum bizygomatic diameter measured as the maximum distance between the two zygomatic arches
  3. Foramen ovale – the longest diameter (‘d1’) and a diameter perpendicular to d1 (‘d2’)
  4. Carotid canal opening on basal aspect – two diameters were taken, one along the long axis of petrous temporal bone (‘d1’) and another perpendicular to d1 (‘d2’).

Areas of foramen ovale and carotid canal were calculated using the formula ‘(Π d1×d2)/4’ or ‘(3.142 × d1 × d2)/4’. Areas of right and left sides were then added to arrive at ‘combined areas’ of foramen ovale and carotid canal. These ‘combined areas’ were considered for further analysis.

For each parameter with male range of ‘a-b’ and female range of ‘c-d’, values ‘a’ and ‘d’ were the ‘identification points’ (referred to as IP hereafter) for females and males respectively. Any skull with parameter reading less than ‘a’ was regarded as female skull and greater than ‘d’ was regarded as male skull. Alternatively stated, for each parameter, if measurements conducted on the skulls of known sex were in the range of a (minimum) to b (maximum) for male skulls, then any skull of unknown sex with value of the given parameter less than ‘a’ was considered as female and thus ‘a’ was regarded as the identification point (IP) of female skulls. Similarly, if for the female skulls of known sex, the measurements ranged between ‘c’ (minimum) to ‘d’ (maximum) then any skull of unknown sex showing the measurement of parameter greater than ‘d’ was regarded as male skull. Value of ‘d’ was regarded as identificated point (IP) for males.

Mean and standard deviations were calculated for the ranges of each parameter of both the sexes. Using these values ‘calculated range’ was arrived at by the formula ‘meant± 3SD’. For a given male calculated range of ‘p to q’ and female calculated ‘r to s’, values of ‘p’ (minimum in male range) and ’s’ (maximum in female range) were chosen as ‘demarking points’ (referred to as DP hereafter) (Singh and Raju 1977, Jit & Singh 1966, Raju et al 1980) for females and males respectively. Skull with measurement lesser than ‘p’ was identified as female skull and greater than ’s’ as male skull. Although IP and DP can identify sex accurately, only 15-25% of skulls can be sexed based on these, as most of the remaining skulls show the measurements in the overlapping neutral zone. Therefore, a ‘limiting point (LP)’ was chosen in this study using multiple trial and error method. Limiting point (LP) is an absolute value found within both ranges. LP was so chosen that vast number of male skulls showed values greater than it and bulk of female skulls showed values lesser than the chosen LP. Hence, as compared to IP and DP, the percentage of skulls that could be identified was far larger with LP. However there was possibility of error as small percentage of make skulls showed values lesser than LP and similarly small number of female skulls showed values greater than LP. To nullify the error combination of two/three parameters was considered. Thus a skull showing values greater that LP in both/three parameters was considered male and that showing values less than LP in both/three parameters was considered female. Although this reduced the percentage of skull that could be identified marginally, the error was nullified.

Observations

Identification point: IP for all the four parameters in either sex are shown in table 1. Maximum number of skulls could be identified using IP of bizygomatic diameter, being 60% of male skulls (IP: 125 mm) and 43% of female skulls (IP: 120 mm). Demarking points: DP of various parameters are shown in table 2. DP of combined area of carotid canal was most efficient parameter in identifying the sex of maximum number of skulls (65% of skulls of either sex). Limiting points: LP of various parameters are shown in table 3. We could not establish a satisfactory limiting point for maximum length of skull. Using the LP of any one parameter, more than 80% of the skulls could be sexed. However, there was an error of 9-28% when only one parameter was used. Thus to reduce the error, multi-variants were considered in combinations (table 4). Only those skulls showing measurements beyond limiting points in both or all the three parameters were considered as definitely male. Likewise, the skulls showing measurements less than limiting points in two or all the three parameters were considered as definitely female. The combination of bizygomatic diameter and combined area of carotid canal could identify the sex of the skull with 100% accuracy. Combination of all the three parameters also yielded 100% accuracy, but could identify lesser number of skulls and hence had no added advantage. The statistical analysis showed that the differences between the sexes in all the parameters were significant.

Discussion

Skull is one of the commonest parts of the skeleton used to opine on the sex of an individual. Sexual dimorphism is insignificant in the pre-pubertal age group. Although adult skulls show a few non-metrical and metrical differences, there is paedomorphic tendency in the human skulls of either sex (William PL et al 1995). Absolute sexual differences seldom exist (Bass 1955). Further, hormones, nutritional status, cultural differences and environmental factors affect these variations. Skulls from different geographical areas vary much. Skull shapes may also vary within a population and even among the closely related.

Traditionally sexing of the skull has been based on the non-metrical traits (Krogman 1962, Berry 1975). Non-metrical differences are mainly in facial skeleton, vault and mandible.

There are a few studies, which have used exhaustive list of metrical parameters for sexing of the skulls (Keen 1950, Hanihara 1959, Steyn and Iscan 1997, Stewart 1948). Keen (1950) has chosen a large number of metrical parameters for sexing of skulls. In his study, the range of maximum length of the skull is 168-198 mm for male skulls and 165-192 mm for females. In Stewart’s series, the range of the maximum length has been 158-210 mm for males and 157-193 mm for females. In our study range is 158183 mm for males and 150-175 mm for females, the skulls of western India population thus showing lesser length than the white population studied by Stewart and cape colored population of Keen’s series.

Maximum bizygomatic diameter in cape colored population ranged from 116-140 mm in males and 104-128 mm in females (Keen 1950). In our study the range was comparable being 120-139 mm for males and 114-125 mm for females.

In addition to maximum length and bizygomatic diameter, we used two new parameters namely, the combined area of foramen ovale and carotid canal openings to sex the skulls.

The identification point (IP) and demarking point (DP) could identify the sex of only around 1525% of skulls (although with a few parameters the percentage was up to 60%). However large numbers of skulls were in the neutral zone of the range and would pose problem in establishing their sex. Thus, we chose limiting point (LP) for bizygomatic diameter (122 mm), combined area of foramen ovale (31mm2) and combined area of carotid canal opening (47.5 mm2). Any skulls with measurements greater than these LP were classified as male and lesser than the LP as female. With limiting point of any one parameter, we could identify the sex of about 80% of the skulls. However, there was an error of 9-20% for different parameters.

To reduce the error, combination of two parameters was considered. Using the limiting points of two parameters, over 70% of male skulls and around 60% of female skulls could be identified. Error dropped to 0-8%. The combination of bizygomatic diameter and combined area of carotid canal was found to be the best, enabling us to identify 75% of male skulls and around 60% of female skulls with 100% accuracy. In addition, in case of fragmented skull, combined area of foramina ovale and/or carotid canal openings may enable us to sex the skulls with reasonable accuracy.

When combination of all the three parameters was considered, only 68% of male skulls and 50% of female skulls could be identified with 100% accuracy. Thus, combination of LP of all the three parameters identifies sex of lesser number of skulls. Therefore we find no added advantage of combination of three parameters over two parameters.

Table 1: Table showing range, mean value and IP of different parameters.

Parameter Sex Range Mean IP % of skulls
Maximum length (mm) M 158-183 171.51 175 18.60
F 150-175 165.57 158 14.28
Bizygomatic diameter (mm) M 120-139 126.75 125 60.48
F 114-125 119.08 120 42.85
Combined area of foramen ovale (mm2) M 25.99-67.40 38.51 49.21 9.30
F 19.58-67.40 29.28 25.99 41.67
Combined are of
carotid canal (mm2)
M 39.28-82.72 57.14 52.73 59.52
F 35.42-52.73 44.46 39.28 16.67

Table 2: Table showing calculated ranges and DP of various parameters.

Parameter Sex Calculated
range
(Mean ± 3SD)
Mean % of skulls
Maximum length (mm) M 153.48-189.54 186.51 0
F 144.63-186.51 153.48 7.14
Bizygomatic diameter (mm) M 113.91-139.59 131.59 9.30
F 106.57-131.59 113.91 7.14
Combined area of foramen ovale (mm2) M 20.58-56.44 44.3 18.6
F 14.26-44.3 20.58 7.14
Combined are of carotid canal (mm2) M 40.52-73.76 53.85 53.68
F 35.07-53.85 40.52 16.67

Table 3: Table showing limiting points of various parameters

Parameter Limiting point Sex Skull beyond LP (%) Error(%)
Maximum length (mm) - M -
F - -
Bizygomatic diameter (mm) 122 M 81.39 14.63
F 85.71 18.18
Combined area of foramen ovale (mm2) 31 M 83.72 28
F 66.67 20
Combined area of carotid canal (mm2) 47.5 M 90.24 15.90
F 83.33 10.26

Table 4: Table showing combinations of parameters in sexing of skull.

Combination
of
parameters
Male
skulls
identified %
Error % Female
Skulls
identified %
Error %
A + B 72.09 3.13 58.33 7.41
B + C 75.61 3.13 66.67 6.67
C + A 75.61 0 58.33 0
A + B + C 68.29 0 50 0

A=Bizygomatic diameter (limiting point=122mm)

B=Combined area of foramen ovale(limiting point=31 mm2)

C=Combined area of carotid canal opening (limiting point=47.5 mm2)

Thus to conclude:

  • Identification point and demarking points of all the parameters could identify the sex of only few skulls leaving a large number of skulls in neutral zone. However, maximum number of skulls could be sexed using IP of bizygomatic diameter (60% of male and 40% of female skulls).
  • Using single parameter, the limiting points could establish sex of about 80% of skulls of either sex albeit with an error of 9-20%. However, when two parameters were considered together 70% of skulls could be sexed with an error of only 0-8%.
  • Among the combinations of parameters, that of bizygomatic diameter and combined area of carotid canal openings gave the best results with 100% accuracy and was able to identify the sex of 75% male and 60% female skulls. Thus percentage of skulls that could be definitely sexed is significantly higher with LP than with using IP or DP.
  • Combination of three parameters did not offer any advantage over combination of two parameters.

Acknowledgements

We are indebted to Prof. Dr. Ajit Shroff, Head, department of Anatomy, Govt. Medical College, Aurangabad for permitting us to use the bones of his department for this study. We sincerely thank Mrs. Gupte and Mrs. Garad for their assistance in statistical analysis.

References

  1. Bass (1995) In http//www.uvic. ca/anth/451/sex_estimation . PDF
  2. Berry AC (1975) Factors affecting the incidence of non-metrical skeletal variants. J Anat. 120:519-535
  3. Hanihara K (1959) Sex diagnosis of Japanese skulls and scapulae by means of discriminal function. J Anthr Soc Nippon 67(722):21-27
  4. Jit I Singh SC (1966) Sexing of adult clavicles. Ind. J of Med Res. 54:551-571
  5. Keen JA (1950) Sex differences in skulls APJA, 8(1):65-79
  6. Krogman WM. In Sex differences in the skull, chapter 5: Sexing skeletal remains. The Human Skeleton in Forensic Medicine. Charles C Thomas, Springfield, Illinois 1962: pp114122
  7. Raju PB, Shamer Singh, Padmanabhan R (1980) Sex determination and sacrum. J. Anat. Soc. India 30(1): 13-15
  8. Singh SK, Raju PB (1977) Identification of sex from the hip bone – demarking points. J. Anat. Soc. India 26:111-117
  9. Stewart TD (1948) Medico-legal aspects of the skeleton. Age, Sex, Race and Stature. APJA 6(3): 315-321
  10. Steyn M, Iscan M (1997) Sexual dimorphism in the crania and mandibles of South African Whites. J Forensic Sci. 42:802-806
  11. Williams PL, Bannister LH, Berry MM, Collins P, Dyson M, Dussek JE, Ferguson MWJ. Gray’s Anatomy In Skeletal System, 38th edition, Churchill Livingstone, New York. 1995: 609-612.
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