osteometry; the measurement of the bones 121 



(d) Miscellaneous 



_ T , ... ., /irv 11N sagittal diameter X 100 



9. Index of the sacral base (10 : 11) - — - r- — 



transverse diameter 



This index, a comparison of the two diameters of the anterior articular 

 surface of the first sacral vertebra, (= Sacral base) has not yet been shown 

 to be of much importance raciallj'. It gives the relative shape of this 

 flat surface, and range from 54.1 in the inhabitants of the Ural Mts. to 

 66.4 in the Burmese. The index for Europeans is estimated at 58.5, 

 but for the Alpine peoples, at 58.7. In Negroes it is 61.2 and in Asiatics 

 in general 62.6. 



III. ANGLES 



Promontory angle; this is the angle formed between the flat surface 

 of the sacral basis and the beginning of the longitudinal curve of the ven- 

 tral surface, as taken in the mid-ventral line, (angle fae, or fac in Fig. 37) 

 This angle is the least in the Tyrolese, 58°; and the highest in Asiatics, 

 averaging, 65°. In the Neolithic station at Schweizersbild are found 

 sacra with a promontory angle of 70°, five degrees more than in any recent 

 race. 



The sacral inclination angle (No. 5 under Pelvic girdle, above) uses 

 the plane of the sacral base for one of its sides, but, as it requires the 

 spino-symphysial plane for the other, must be taken only on a complete 

 girdle. Another form of the Promontory angle, which is in some ways 

 more satisfactory than the one given here, might be made by using, with 

 the same plane of the sacral base, the entire straight length line instead 

 of the one indicating the anterior portion of the ventral surface, i.e., 

 the line ab of Fig. 37 rather than the line ae of the same figure. This 

 line seems not to have been used, and is hence not recommended 

 here. 



Other angles suggested, and occasionally used, are (1) the angle formed 

 by the plane of the two auricular surfaces, usually meeting along an im- 

 aginary line posterior to the bone, and (2) the angle of inclination of 

 the sacrum, or of the sacral axis, when the subject is standing. This 

 latter, like that of the inclination of the pelvis as a whole, can be measured 

 only upon the living subject, and then only approximately. 



It might be possible, however, to relate the sacrum to some definitely 

 determined plane in a properly articulated pelvic girdle, such as the spino- 

 symphysial plane or that of the rim of the lower pelvis, and thus obtain 

 proportions or relations of importance. 



Anatomical variations in the sacrum, such as the number of the verte- 

 bras which compose it, or the sacralization of the last lumbar vertebra, 

 are mainly of biological interest, as are similar variations in other bones, 

 and seem to have no racial significance. 



