spite of the higher frequency of 6-piece sacra iri San females than in San males.

Transcription

1 258 spite of the higher frequency of 6-piece sacra iri San females than in San males. 4. The Degree of Sexual Dimorphism of the Sacrum in the Various Ethnic Groups The question is posed as to whether some population groups are consistently more sexually dimorphic than others. Table 90 sets out the number of sex differences in both 5-piece arid piece samples of N. Nguni, C. Nguni, Sotho and San s=>cra. The corresponding information in the combined S.A. Negro sample is given in Table 87. In the S.A. Negro sub-groups, it would seem that in piece sacra, the N. Nguni with nine significant sacral sex differences (at the 1% limit of significance) are the most sexually dimorphic, followed by C. Nguni (6), Sotho (5) and finally, San (2). It is possible that different relative frequencies of 6-piece sacra in male and female groups might influence metrical results, unless the groups being compared have approximately equal frequencies of 6-piece sacra. The frequency of 6-piece sacra in the samples upon which the metrical analysis was conducted, is consistently higher in male than in female sacra in each Negro subjet (Table 28, p.93), though the male preponderance is more apparent in C. Nguni and N. Nguni than in Sotho sub-groups (male - female differences are 14,9%, 11,0% and 4,0% respectively). It is noteworthy, however, that the frequency of 6-piece sacra in the N. Nguni female sample (15,9%) is the lowest of all the female ethnic groups. When sex differences are examined in "pure" 5-piece sacra (Table 90), there are 6 significant sex differences apiece in both N. Nguni and Sotho, fewer (4) in the C. Nguni and least in the San (2). It has been shown in Chapter 6 that 6-piece sacra ha/e certain 'male' characteristics, including those of increased length and relative narrowing. It is possible therefore, tnat the presence of relatively few 6-piece sacra in the N. Nguni female piece sample has, in effect, made more apparent some of the 'female' characteristics in the sample. The comparisons of individual mean characters among the tribal sub-groups in Chapter 5 show, that in piece samples, the N. Nguni female sacra tend to be the shortest (Tables 12, 13) and the broadest, both relatively and absolutely (Tables 18-21), of the three tribal groups though only the difference between N. Nguni and Sotho female sacra for absolute and relative anterior breadth is significant. However, in

2 259 the 5-piece samples (Table 29, p. 94) the N. Nguni female sacra are no longer the shortest nor the broadest as measured by greatest breadth (GB). Instead, the Sotho female sacra now have the shortest mean curved and straight length and the C. Nguni the highest mean greatest breadth. In addition, though the mean values for the index of anterior breadth to length and the index of greatest breadth to length show the N. Nguni sacra still to be the broadest, the differences are minimal and are not significant. Only the mean measure of absolute anterior breadth remains significantly greater in N. Nguni than in Sotho female sacra. Thus, the presence of relatively few 6-piece sacra in the N. Nguni female sample (as compared with C. Nguni and Sotho) has seemingly increased the sexual dimorphism of the N. Nguni sample by emphasizing some of the 'female' characteristics namely, decreased length and increased absolute and relative breadth of the N. Nguni sacra. This high degree of sacral sexual dimorphism in N. Nguni as compared with the low degree exhibited by the San sample (Table 9C) has, in turn, influenced the San-S.A. Negro relationships demonstrated by the metrical analysis. As discussed in Chapter 5, D3, the two extremes of sexual dimorphism (highest in N. Nguni, lowest in San) seemingly contribute to a closer N. Ngurii-San male metrical relationship in piece sacra, whilst apparently increasing the distance between N. Nguni and San female piece sacra. Overall, the sexual dimorphisn. is the highest in the combined S.A. Negro sample (Table 89) where there are 10 significant differences in the piece sample and 8 in the 5-piece sample, and least in the San with 2 significant differences in both piece and 5-piece samples. However, these total sex differences in the various groups include al1 measures and indices and thus, dependent variables, the totals are reduced to independent variables by eliminating covering measures and indices, analysis of the piece samples reveals that there are three differences wh'_.h are common to all groups namely, sacral index A (100 ASB/L), the corporo-basal index (100 tr.bo./gb) and the anteroposterior diameter of the body of SI. The N. Nguni sub-group has two additional independent variables (length and the promontory angle), the C. Nguni one (relative depth of curvature) and Sotho one (length). Thus the N. Nguni sub-group has a slightly higher number of sex differences than C. Nguni or Sotho on analysis of independent variables.

3 260 In 5-piece sacra, two variables show sex differences which are common to all three sub-groups of the S.A. Negro, namely, the corporobasal index a J the anteroposterior diameter of the body of S I. The N. Nguni have two additional variables (anterior breadth and the sacral index) as do the Sotho (length and relative anterior breadth) and the C. Nguni only one (anterior breadth). Thus, the pattern in 5-pi«_wc samples is similar on analysis of both dependent and independent variables. In sum, the analysis of piece sacral s'atnples reveals that the N. Nguni sub-group of the S.A. Negro series is consistently more sexually dimorphic than the C. Nguni and Sotho sub-groups, both on consideration of all metrical characters and also when covering measures and indices are eliminated from the analysis. The C. Nguni in turn, show somewhat more sexual dimorphism than the Sotho sacra. The analysis of the 'pure' 5-piece samples, however, shows a similar degree of sacral sexual dimorphism in N. Nguni and in the Sotho, and both subssts show slightly more sacral sexual dimorphism than the C. Nguni sample. The analysis shows that the San are consistenfy less sexually dimorphic than any one sub-group and the combined S.A. Negro series. TABLC 90 Sex Differences in 5-piece and piece Samples of N. Nguni, C. Nguni and Sotho and San Sacra. N. Nguni C. Nquni Sotho San S "5-6 b b cl L hmc ASB GB ap.bo. SI tr.bo. SI L/cL 100 hmc/l pmc/l ASB/L GB/L a p. bo. A r.bo tr.bo./gb L P Total significant sex differences indicates a significant sex difference present at the 1% limit of significance.

4 Discussion of Sex Determination by the Sacrum The characters which strikingly and significantly distinguish between the sexes in S.A. Negro sacra are the measures of the body of SI and the corporo-basal index (100 tr.bo./gb) all of which are significantly greater in male sacra. In the less sexually dimorphic San sacra, the corporo-basal index is the most reliable character for determination of sex. The next most useful characters for sex determination are anterior straight breadth and the proportion of anterior breadth to length (100 ASB/L), both of which are significantly greater in females. The absolute and relative measure of greatest breadth, however, is not such a good arbiter of sex. A possible reason for this may be that the termini used for measuring ASB lie on the linea arcuata: this line bounds the pelvic inlet, the shape and size of which are markedly influenced by sex (Caldwell and Moloy 1933, Greulich and Thoms 1944, Thoms 1956). Thus, anterior breadth and the associated index may be a more sensitive indicator of sex than the measure of greatest breadth. The absolute measures of sacral length (cl,l) are significantly greater in male than in female sacra, though the t-values are not as high as for the preceding measures. Less significant but still of value is the point of maximum curvature relative to length which is significantly more caudally placed in male than in female sacra. The promontory angle, too, may be of value in assessing sex. The angle is greater in male sacra and the significance of this finding may be that the smaller angle in females tends to throw the sacrum further back, that is, incline it more posteriorly, and thus increase the size of the birth canal. Heyns (1945) found that the female sacrum is inclined more posteriorly than the male sacrum in the pelvis. He measured this inclination by considering the pubo-sacral diameter, which, he found was less in male pelves. It is evident that variation of sacral inclination in the pelvis is owing, in part at least, to variation in the promontory angle. Oavivongs (1963) is his study of 50 male and 50 female aboriginal 5-piece sacra and pelves (Table 39, p.121) found that the index of the transverse diameter of the body of SI to greatest breadth was the best indicator of sex in the sacrum. In addition, he found statistically significant differences between male and female for the mean index of greatest breadth to length, for straight and curved length, for the diameters of the body of SI but not for the related index of the sacral

5 262 base nor for the measure of greatest breadth. He notes that the measure of greatest breadth is not a good indicator of sex, as was found in this study; he did not, however, measure anterior breadth1 and we cannot compare findings for the two measures of breadth. Fawcett (1938) first devised the index of the transverse diameter of the body of SI to greatest breadth. He named it the corporo-basal index and he tested it on 213 Caucasoid and 196 American Negro sacra of known sex (Tables 38, 38a, pp. 117, 118). He found it a reliable indicator of sex and attributed this finding to the smaller width of the body of SI in females as compared with males. echoed in anatcnical texts such as Gray's Anatomy (1964). This reason is Grant's Method of Anatomy (1971), however, states the additional reason for the success of this index as an indicator of sex, namely, that the body of SI is not only smaller in female than in male sacra but the breadth of the base is usually greater in female than in male sacra. Thus, the combination of the two measures, one greater in female sacra (greatest breadth) and the other smaller in female sacra (transverse diameter of SI) further separates the mean values of the index for males and females. This the usefulness study, then, supports and extends Fawcett's finding on of the corporo-basal index for sex determination. In addition, the study shows that in a population group which shows little sexual dimorphism, as for example the San, the corporo-basal index may be the only metrical character which is of value in sex 2 determination by the sacrum. Note on the Curvature of the Sacrum The results of the present study show that the mean height of maximum curvature is less in the female than in the male sacrum in both the S.A. Negro and San samples, though the differences are not significant. Similarly, when curvature is assessed by the index of straight length to curved length (length-curvature index A), the means are slightly higher in female sacra (i.e. they are less curved) than in male sacra in both the S.A. Negro and the San but the differences are not significant. These tendencies in the male and female sacra are ^see footnote on p. 123, Chapter 5. 2 The corporo-basal index in the San female pelvis with an ischium-pubis index of 93,1 / (see addendum, p. 39) is 38,9*. This is the lowest value in the San series and thus supports the diagnosis of female in the skeleton.

6 263 confirmed when the sacra are sorted into categories of sacral curvature (Table 15c, p.66); there are more female than male sacra in t.he categories of slight and moderate curvature in both the S.A. Negro and San samples. The results are not, however, significant by the chi-square test at the 1% level. The mean position of maximum curvature relative to length is lower in male than in female sacra in both S.A. Negro and San sacra, though the difference is significant only in the S.A. Negro sample. One of the earliest reports on the curvature of the sacrum is by Warren (1897, cited by Trotter 1926) who found in a series of Ancient Egyptian sacra, that many of the male sacra were strongly curved, whilst a considerable number of the female sacra were nearly flat. Paterson (1892) examined Caucasoid sacra of known sex and found only slight differences of sacral curvature between male and female. He noted, however, that the sacrum was more often deeply curved in the upper part in female than in male sacra, and, that the absolute depth (or height) of curvature was greater in the male than in the female. Trotter (1926) confirmed Paterson's findings but noted that the differences between male and female sacra in her series of Egyptian sacra were so slight as to be of no aid in sexing a sacrum. The present study of the S.A. Negro sacrum confirms the tendencies reported by Paterson (1892) and Trotter (1925) for female secra to be less curved than male sacra and for the position of maximum curvature to be higher in female than in male sacra. As in the previous studies, however, the results are not significant. B. SEXUAL DIMORPHISM OF NON-METRICAL FEATURES OF THE S.A. NEGRO SACRUM There is a higher frequency of 6-piece sacra in male than in female S.A. Negro sacra and this trend is present in each sub-sample of the S.A. Negro series. No one of these differences is, however, significant at P< 0,01. Transitional features at the superior border of SI, i.e. alar facets on SI occur with approximately equal frequency in male and female sacra. Transitional features in SI at the S1/S2 junction are present significantly more often in 5-piece female than in 5-picce male sacra and there are absolutely and relatively more such female (33/117, 28,2%) than male 5-piece sa^ra (24/159, 15,1%). In 6-piece sacra, transitional features at the S1/S2 junction, too, are present more often in female

7 264 than in male sacra though the difference is not significant at the 1% level. Female sacra, too, have a slightly higher frequency of transitional features of the vertebral arches of SI and S2 in both 5-piece and 6-piece sacra but the differences between male and female are not significant. Transitional features in the last piece of the sacrum are present almost exclusively in 6-piece sacra in the form of 5/6-piece sacra. There is no significant sex difference i the frequency of 5/6-piece sacra. No significant sex differences are present in the frequencies of any of tlie categories of basal ity. Synostosis of Co 1 to the sacrum is present significantly more frequently in female (24,8%) than in male S.A. Negro sacra (14,9%) and the higher frequency in females is present in each decade of adult life. This finding is in contrast to a previous report (Trotter and Lanier 1945) that sacrococcygeal synostosis is commoner in males than in females in both American Caucasoid and Negro sacra. Transitional features at the S1/S2 junction A possible explanation for the higher frequency of transitional features in SI at the S1/S2 junction in female sacra may be related to the finding by Bornstein and Peterson (1966), de Beer Kaufman (1974) and other workers, that females lend to have a shorter presacral column of 23 PSV, whereas males tend to have an increase in presacral vertebrae to 25. It could be predicted that female spines with 23 PSV might be expected to show evidence of sacralisation of the 24th vertebra. Analysis of the columns with 23 PSV (Table 84, Chapter 9) shows that whilst there are relatively more female spines (7,5%) than male spines (5,6%) with 23 PSV, transitional features are present as frequently in the male as in the female spines with 23 PSV. Transitional features are in fact, presen* slightly more frequently in the male (13/14 spines) than in the female(9/12) spines. ' Moreover, transitional features are present in SI in spinal columns with the formula 24 PSV + 5S and are relatively more common in female than in male spines (30/105, 28,6%; 20/127, 15,8% respectively). Thus, the hypothesis that the higher frequency of transitional features in SI in female sacra is due to a sacralising effect on the 24th vertebra is not supported. A factor which might account for or influence the higher frequency

8 265 of transitional features in SI in female sacra is the sex-difference in the number of sacral pieces participating in the sacro-iliac joint. This was suggested to me by Tobias (personal communication 1974). It has been shown by Derry (1912), in a sample of 97 Caucasoid sacra, that it is usual for the sacral auricular surface to be smaller in the female than in the male sacrum; in female s; era it is usually limited to the first two sacral pieces. The findings in the S.A. Negro sacrum (Gillman 1929, de Beer 1962) are in accordance with Derry's conclusion that the extent of the auricular surface in the female sacrum is smaller than in the male sacrum. It has been further shown (de Beer, 1962), on a large sample of sacra (n - 318), that the auricular surface in the S.A. Negro female sacrum extends mo^e frequently as far as the middle of the third sacral piece (62,3%), whereas n the majority of male sacra (62,9%) it extends beyond this point, over 23/4 sacral vertebrae or more. The possibility is suggested, therefore, that transitional features in SI tend to occur more frequently when the sacro- 1iac articulation area is of reduced extent, as in female sacra. When the data for 5- and 6-piece S.A. Negro sacra are examined (de Beer 1962), it is notable that, in 5-piece sacra, 67,0% of female and only 48,9% of male sacra have auricular surfaces that extend over 2J sacral vertebrae. If this finding is correlated with the present findings, a relationship is suggested between 5-piece sacra, reduced sacro-iliac articular area and transitional features in SI in female sacra. Thus, there may be some factor operating during the presumed individuation of sacral vertebrae by the ilium which, when a 5-piece sacrum is induced in conjunction with a lessened sacro-iliac articular area, tends to produce transitional features in bl C. SEXUAL DIMORPHISM OF VERTEBRAL NUMERICAL VARIATION IN THE SOUTH AFRICAN AND AMERICAN NEGRO AND THE SAN There is a higher frequency of 6-piece sacra in males than in females in the S.A. Negro (male 33,1%, female 23,6%) and the American Negro (male 29,2". female 20,4%) and indeed, in all population groups surveyed, save for the San sample of the present study (male 12,9%. female 18,2%, Table 9). None of these sex differences is, however, significant at the 1% level. It is possible that the small San male sample of the present study may be unrepresontative, since it is the only sample which shows a female preponderance of 6-piece sacra.

9 266 Indeed, in the San sample of Duparc (1942), the frequency of 6-piece sacra is, as in other population groups, higher in male (31,3%) than in female sacra (16,7%). There is a higher frequency of an increase in total precoccygeal vertebrae in males than in females in the S.A. Negro, the American Negro and the San. The sex differences in the two Negro groups are significant. This trend is present in each of the S.A. Negro subsets and in all the populations surveyed (see Chapter 9). However, a decrease in total precoccygeal number (which occurs relatively infrequently), is present more often in females than in males in the S.A. Negro (including each of its subsamples), the American Negro and the San and in most of the populations surveyed. Thus, males and females show opposite tendencies in the spinal column, the female being more likely to show a decrease and the male an increase in total PCV. As discussed in Chapter 4, Bornstein and Peterson (19G6) suggested that variation in presacral vertebral number may be a sex dependent characteristic and that females are more likely to have a shorter presacral column and males a longer column. This tendency towards a decrease in number of vertebrae in females and an increase in males is demonstrated in the present study for total precoccygeal vertebrae in the South African and American Negro and the San, for sacral vertebrae in both Negro groups and, in a previous study, for presacral vertebrae in S.A. Negroes and San (de Beer Kaufman 1974). D. SUMMARY AND CONCLUSIONS The analysis of the mean metrical characters reveals that South African Negro male sacra are, in general, significantly longer than female sacra. The curvature of the sacrum tends to be deeper in males than in females though this trend is not significant. The mean position of maximum curvature is significantly more caudally placed in male than in female sacra. Male sacra are, in general, absolutely and relatively narrower than female sacra and sacral index B shows that 67,8% of female sacra are platyhieric whilst 53,7% of male sacra are either dolichohieric or subplatyhieric. This finding is significant. The measure of anterior breadth and the related sacral index A is a better indicator of sex than is the measure c> greatest breadth and the related index of greatest breadth to length (sacral index B). m i v

10 267 The body of SI is significantly larger in male than in female sacra for both the mean transverse and anteroposterior diameters. The corporo-basal index shows marked sexual dimorphism. The mean promontory angle is greater in male than in female sacra. Analysis of sex differences in the total piece samples of the various ethnic groups reveals that the pooled S.A. Negro sample has the highest degret of sexual dimorphism of metrical features and the San the least. The N. Nguni sub-group of the S.A. Negro series too, shows a high degree of sexual dimorphism, though somewhat less than in the combined S A. Negro sample. The N. Nguni piece sacra are more sexually dimorphic than the C. Nguni or Sotho sacra. San sacra are consistently less sexually dimorphic than any one sub-group as well as the combined S.A. Negro sample. It has been shown in Chapter 6 that 6-piece sacra show considerably less sexual dimorphism than 5-piece sacra. Analysis of sex differences in 5-piece sacra and piece sacra shows, however, that the higher degree of sexual dimorphism in the S.A. Negro than in the San is not altered to any appreciable extent by the exclusion of 6-piece sacra from the samples. The higher degree of sexual dimorphism in the N. Nguni than in the C. Nguni or Sotho sub-groups in piece samples is not, however, apparent in 5-piece samples. This is owing mainly to a relatively tow frequency of 6-piece sacra in the N. Nguni female sacra. Sexual dimorphism of non-metrical features of S.A. Negro sacra is not marked, save for a significantly higher frequency of transitional features in SI at the S1/S2 junction in 5-piece female than in 5-piece male sacra and a higher frequency of synostosis of Co 1 to the sacrum in females. There are no significant differences in the frequency of transitional features at the L5/S1 junction or at the S5/S6 junction. The categories of basality are not differently distributed in male and female sacra. Curvature, which is often assessed non-metrically, has been shown by the.iietrical analysis, to be less in female than in male sacra, but the results do not reach the 1% level of significance. The position of maximum curvature tends to be more cranially placed in female than in male sacra and the trend is significant. A non-metrical feature which may be of value in assessing the sex of a sacrum is the extent of the sacral auricular surface. This feature was examined in a previous report (de Beer 1962) and the results show that the sacral auricular surface extends over two and three-quarter

11 268 sacral vertebrae or more in the majority of male sacra (62,9%), whereas in the majority of female sacra (62,2%) it extends over only 2\ sacral vertebrae or less. The difference is significant at P< 0,01. There is a higher frequency of 6-piece sacra in males than in females in the pooled S.A. Negro sample as well as in each subset of the series and in the American Negro sample. This male preponderance of 6-piece sacra is not, however, significant. There is a significantly higher frequency of an increase in total precoccygeal vertebrae in males, whereas, females more commonly have a decreased number of precoccygeal vertebrae. This finding is present in the South African and American Negro, and the San. The San sacra show significant sex differences for the corporo-basal index and the transverse diameter of the body of SI. Sex differences are not significant, however, for certiin other parameters which have teen demonstrated as showing sexual dimorpnism in the S.A. Negro series. These are length, anterior breadth, the sacral indices and the anteroposterior diameter of the body of SI. Whilst this finding seems to indicate a lower degree of sexual dimorphism in the San, it is not inconceivable that, a possible misdiagnosis of sex in four or possibly five sacra (see addendum, page 39) might account, in part at least, for these results.

12 r 269 C H A P T E R lj_ G ENERAL CONCLUSIONS In this chapter, section A sunniarises the metrical features of the S.A. Negro and San sacra, the non-metrical features of the S.A. Negro sacra and the related spinal formulae, and the numerical constitution of the S.A. Negro, San and American Negro sacra and precoccygeal vertebrae. Section 6 gives the general conclusions about the inter-relationships between S.A. Negroes and San and among the S.A. Negro tribal groups, in the light of the findings of the motrical analysis of the sacra and the analysis of numerical variation of vertebrae. Section C deals with sexual dimorphism of the sacrum and of variation in vertebral number. Section D presents the non-metrical features of the sacrum and vertebral columns from a developmental and morphological viewpoint. Section E is the summary. Chapter 11 is thus presented under the following headings:- A. The Characteristics of the Sacrum and Vertebral Column. 1. The metrical characteristics of the S.A. Negro sacrum 2. The metrical characteristics of the San sacrum 3. The non-metrical features of the S.A. Negro sacrum 4. Numerical characteristics of the S.A. Negro vertebral column 5. Numerical characteristics of the San sacrum and precoccygeal vertebral column 6. Numerical characteristics of the American Negro sacrum and precoccygeal vertebral column. B. Intertribal and Inter-group Relationships. 1. Intertribal relationships and the relationships between S.A. Negro and San sacra as determined by the sacral metrical analysis 2. The relationships between S.A. Negro, San and American Negro as displayed by vertebral numerical variation C. Sexual Dimorphism of the Sacrum and Precoccygeal Vertebral Column D. Developmental ana Morphological Aspects of the S.A. Negro Sacrum and Vertebral Column

13 270 *l. Presacral and sacral vertebrae 2. Basality 3. Sacrococcygeal synostosis E. The Summary. A. THE CHARACTERISTICS OF THE SACRUM AND VERTEBRAL COLUMN 1. The Metrical Characteristies of the South African Negro Sacrum The features of the South African Negro sacra reveal no major intertribal differences. * he tribal groups are thus pooled to provide a sample representative of the S.A. Negro. The sacral characteristics of the pooled population of piece S.A. Negro sacra (but with references to the characteristic features of 6-piece sacra where relevant) may therefore be summarised as follows (Table 91). The length of the S.A. Negro sacrum is variable and the mean curved length is 111,6 in male and 106,6 mm in female sacra (range = mm). The mean straight length is less, being 100,3 mm in male and 95,9 mm in female sacra. As might be expected, length is significantly greater in 6-piece than in 5-piece sacra and this applies to both curved length (males 121,8 and 108,1 mm, females 120,0 and 104,3 mm respectively) and straight length (males 109,2 and 97,3 mm, females 107,3 and 94,2 mm respectively). The curvature of the sacrum expressed as absolute height of curvature, is, on the average, 19,0 mm in males and 17,6 mm in females. When assessed by relative height of curvature it is,on the average, 19,6% in male and 18,5/ in female sacra. Six-piec^ sacra> both male and female, have a significantly greater absolute but not relative height of cu-vature than 5-piece sacra. Longer sacra thus have a proportionally greater absolute height of curvature. When longitudinal curvature is ssessed by the index cf straight length to curved length, the mean velues in the total sample of piece sacra are 89,8% in males and 90,OX in females. The nv an values are similar, too in 6-piece sacra in both males (89,6%) and females (89,4%). The majority (76,4:;) of S.A. Negro male sacra have either marked (36,9!'.) or moderate (39,5%) curvature, whilst only 12,3% show strong curvature and 11,3% slight curvature,.n females, most sacra (52,1%) are moderately curved, or less often (34,7%) markedly curved, whilst few are strongly curved (8,3 ) or slightly curved (4,9%).

14 271 TABLE 91 The Mean Dimensions of 4-5-^,-piece Male and Female S.A. Negro Sacra Mai e Female Mean ± S.E. Range n Mean + S.E. Range n curved length (cl) m, 6 ±, ,6±, straight length (L) 100,3±, ,9±, height of max. curvature 19,0±, ,6±, L/cL 89,8±,29 76,2-98, ,0±,31 80,7-98, U0 hmc/l '9,6±,43 7,0-48, ,5±,44 5,5-32, pinc/l o 5,2 ±,54 42,0-86, ,7±,67 39,1-82,0 121 anterior breadth (ASB) 92,4±, ,9±, greatest breadth (GB) 105,1±, ,4±, ASB/L 93,0±,75 65,7-120, ,6±1,06 71,7-132, GB/L 106,2±,79 84,2-137, ,6±1,06 82,7-129,3 118 ap.dia.body of SI 32,1 ±, ,0±, tr.dia. body of SI 52,3±, ,0±, ap.bo./tr.bo. 6 1,5±,33 49,1-76, ,8±,46 50,0-74, tr.bo./gb 49,8±,27 40,0-60, ,3±,34 35,6-56,8 119 L P 56,8±, ,1 ±, The position of maximum curvature relative to length is more caudally placed in male (65,2*) than in female (62,7%) sacra. The mean anterior straight breadth of the total S.A. Negro series is 92,4 mm in male and 96,9 mm in female sacra, whilst relative anterior breadth shows a relatively long and narrow sacrum in males (93,0%) but less so in females (101,6%). The measure of greatest breadth is, without exception, greater than anterior breadth in all sacra measured, and the mean greatest breadth is 105,1 irrn in male and 106,4 mm in female sacra. The mean relative breadth (the sacral index of Turner) reveals platyhiery in male sacra (106,2%) and marked platyhiery (111,6%) in female sacra. Almost half (46,3%) of the male sacra are relatively broad or platyhieric and approximately equal numbers of sacra are either relatively long and narrow (dolichohieric,(54 or 28,7%) or subplatyhieric (47 or 25,0%). The great majority of female sacra (67,8%) fall into the platyhieric category and the remainder ure either subplatyhieric (18,6%) or dolichohieric (13,C The mean absolute breadth of 6-piece sacra is but little different from that in the total piece sample, but 6-piece sacra are relatively narrow in comparison with the total sample, the mean index of anterior breadth to length being 84,9% in males and 89,6% in females and the mean sacral index of greatest breadth to length being 97,5% in males and 100,4% in females.

15 272 The mean anteroposterior diameter of the body of SI is 32,1 mrn in male and 29,0 mm in female sacra, whilst the mean transverse diameter of the body of SI is 52,3 mm in male and 48,0 mm in female sacra. The 6-piece sacra have a significantly greater mean transverse diaireter of SI than 5-piece sacra in males (t=2,924) and probably in females (t=2,358). The mean sacral base index (the index of the anteroposterior diameter to the transverse diameter of SI) is 61,5% in male and 60,8% in female sacra. The corpo'o-basal index has a mean value of 49,8% in male sacra, indicating that tie width of the body of SI is roughly cne-half or more of the greatest breadth of the sacrum, whereas, in females, the mean value for the index is 45,3% which indicates that the width is, on the average, less than one-half of the greatest breadth. The mean angle of the promontory is 56,8 in males and 54,1 in females. Male 6-piece sacra have a significantly greater promontory angle (61,4'J) than 5-piece (54,80, t=6,517). The comparative metrical analysis of the dimensions of 5-piece and 6-piece S.A. Negro sacra shows that, in consequence of the additional vertebra, both male and female 6-piece are longer in general and relatively narrower, with a greater absolute but not relative mean height of curvature than 5-piece sacra. Male 6-piece sacra, too, have a significantly greater mean absolute and relative width of the body of SI and a greater mean promontory angle: a similar trend in female sacra is not significant. 2. The Metrical Characteristics of the San Sacrum The dimensions of the San sacrum are, in general, small in accordance with their small stature and small bodily dimensions. The mean dimensions of the San sacra are given in Table 92 and are summarised as follows. The mean curved length of the San sacrum is 103,0 mm in male and 99,5 nm in female sacra, whilst the mean straight length is less, being 93,8 mm in male and 91,4 mm in female sacra. These values are the lowest for any of the population groups reported )n in this study. Curvature of the San sacrum is shallow and ' mean absolute height of curvature is 16,1 mm in male and 14,9 mm in <e sacra. This shallow curvature is reflected, too, in the mean relative height of curvature which is 17,5% in male and 18,7% in female sacra, ihe results for longitudinal curvature, which is assessed by the index of straight length to curved length, show on the average moderate curvature in both male (90,8%) and female (91,6%) sacra. When, however, the sacra are

16 273 sorted into categories of longitudinal curvature, almost all male sacra are either markedly (44,8%) or moderately (44,8%) curved,while female sacra fall equally into the categories of slight (27,8%), moderate (38,8%) and marked (27,8%) curvature. The mean value for the position of maximum curvature relative to length is 63,7% in male and 59,7% in female sacra. TABLE 92 The Mean Dimensions of piece Male and Female San Sacra Mai e F ema1e Mean ±S.E. Range n Mean ±S.E. Range n cl 103,Oil, ,5± 2, L 93,8±2, ,4i2, hmc 16,1±, , 9±1, L/cL 90,8±,59 84,2-96, ,6±,97 80,5-99, hmc/l 17,5±,92 7,3-24, ,7 ±1,73 8,0-39, pmc/l 63,7±1,07 56,0-77, ,7+1,99 43,5-78,2 18 ASB 81,4+, ,1±1, GB 92,8±1, ,3±1, ASB/L 88,1±2,08 68,3-107, ,5i3,07 64,2-129, GB/L 99,9±1,97 81,6-120, ,6±3,23 73,3-138,8 18 ap.bo. 27,9±, ,7±, tr.bo. 45,6±, ,6±, ap.bo./tr.bo. 6 1,5±,84 51,9-68, ,8±1,07 53,2-71, tr.bo./gb 49,2±,65 42,7-55, ,3±,90 38,9-52,7 21 L P 56,1±, ,7±1, The San sacrum is both absolutely and relatively narrow when measured by anterior breadth (mean breadth = P i,4 mm in males and 84,1 mm in females, mean relative anterior breadth = 88,1% in males and 93,5% in females). The mean greatest breadth is 92,8 mm in males and 94,3 mm in females. The sacral index of greatest breadth to length gives a mean value which lies at the upper limit of dolichohiery in male sacra (99,9%) and of subplatyhiery in female sacra (104,6%). When the sacra are sorted into the categories of the sacral index, more San male sacra (43,3%) fall into the dolichohieric class than into the subplatyhieric class (26,7%) or the platyhieric class (30,0%), whilst female sacra are

17 274 more generally subplatyhieric (41,0%) or platyhieric (35,4%) and less often dolichohieric (23,6%). The dimensions of the body of SI in San sacra are small for both anteroposterior diameter (males 27,9 mm, females 26,7 mm) and transverse diameter (males 45,6 mm, females 42,6 mm). The mean sacral base index is similar in male (61,5% and female sacra (62,8%). The corporo-basal index has a mean value of 49,2% in male and 45,3% in female sacra. This mean angle of the promontory is 56,1 in male and 54,7 in female sacra. I 3. The Non-metrical Features of the S.A. Negro Sacrum The S.A. Negro sacrum usually consists of 5 conjoined vertebrae but is commonly increased to 6 pieces (males 33,1%, females 23,6%) and less often decreased to 4 pieces (males 2,8%, females 1,9%). The first piece of the sacrum shows great variation owing to its being in a transitional spinal region. The variations m?y be either at the L5/S1 junction or the S1/S2 junction or, rarely, at both positions. Alar facets, which may be present on the superior surface of SI, signify evidence of transition at the I5,/Sl junction and are found in 5,6% of all male sacra (two 4-piece and twelve 5-piece sacra) and 3,2% of all female sacra (one 4-piece and four 5-piece s?cra). The region between the bodies of SI and S2 shows minor separation in the form of a ridge or slit in 13,2% of 5-piece male and 19,7% of 5-piece female sacra and in 19,6% of 6-piece male and 13,5% of 6-piece female sacra. Such signs of minor separation are not regarded as evidence of transition at the S1/S2 junction in this study for the reasons c ven in Chapter 8. However, a major degree of separation, such as a ridge plus a slit, or the partial or complete separation of the bodies of SI and S2, _i_s regarded as a transitional feature. Such major separation occurs in 7,5% of 5-piece male and 23,1% of 5-piece female sacra and 23,2% of 6-piece male and 43,0% of 6-piece female sacra. Thus, it is more common in female than in male sacra and in 6-piece than in 5-piece sacra. A second promontory, which is also regarded as a transitional feature, is not found in any 5-Diece sacrum but is present in some 6-piece sacra (14,6% of male and 18,9% of female sacra). No reports on the frequency of a second promontory or on the occurrence of a second promontory in relation to the number of sacral pieces were found in the literature available to me.

18 Author De Beer Kaufman P M Name of thesis A study of the sacrum and some aspects of presacral vertebrae in San (Bushmen) and Southern Africa and American Negroes 1975 PUBLISHER: University of the Witwatersrand, Johannesburg 2013 LEGAL NOTICES: Copyright Notice: All materials on the University of the Witwatersrand, Johannesburg Library website are protected by South African copyright law and may not be distributed, transmitted, displayed, or otherwise published in any format, without the prior written permission of the copyright owner. Disclaimer and Terms of Use: Provided that you maintain all copyright and other notices contained therein, you may download material (one machine readable copy and one print copy per page) for your personal and/or educational non-commercial use only. The University of the Witwatersrand, Johannesburg, is not responsible for any errors or omissions and excludes any and all liability for any errors in or omissions from the information on the Library website.