420 THE ANATOMY OF VERTEBRATED ANIMALS. 



moner among the Bushwomen of South Africa than else- 

 where. 



But it is in the skull that the different races of mankind 

 present the most striking osteological differences. The pro- 

 portions of the antero-posterior and the transverse dimensions 

 of the brain-case vary extremely. Taking the antero-posterior 

 diameter as 100, the transverse diameter varies from 98, or 99, 

 to 62. The number which thus expresses the proportion of 

 the transverse to the longitudinal diameter of the brain-case 

 is called the cephalic index. Those people who possess crania 

 with a cej^halic index of 80 and above are called hracJiy- 

 cephali ' those with a lower index are dolichocephaU. The 

 brain-case also varies greatly in its relative height. The pro- 

 portion of the length of the cerebral chamber to the basicranial 

 axis (as 100) may rise to 270 in the higher, and sink to 230 in 

 the lower races ; and there are great diversities in the extent 

 to which the cerebral cavity is rotated backward or forward 

 upon this axis. The position and the aspect of the occipi- 

 tal foramen vary considerably, as does the plane of that part 

 of the squama occipitis which lies above the superior semicir- 

 cular ridge. The supra-ciliary ridges vary greatly in their 

 development, and in the extension of the frontal sinuses into 

 them. They are nearly or quite solid in many Australian skulls. 



In the size, form, and disposition of the facial bones, the 

 different races of mankind present great diversities. A line 

 drawn from the anterior extremity of the premaxilla to the 

 anterior extremity of the basicranial axis, may be taken to 

 represent the facial axis, and the angle included between 

 these two is the craniofacial angle. It varies with the extent 

 to which the face lies in front of, or below, the anterior end of 

 the cranium, from less than 90° to 120°. When it is great, 

 the face is progyiathoiis ; when it is small, the face is ortJiog- 

 nathous. This is the fundamental condition of prognathism 

 or orthognathism^. A secondary condition is the form of the 

 alveolar portion of the upper jaw, which, so far as it is ver- 

 tical, tends toward orthognathism ; but, so far as it is oblique 

 and produced, tends to prognathism. 



The arch formed by the teeth is, in the most orthogna- 

 thous races, wide and evenly rounded ; while, in the most 

 prognathous, it is prolonged, and its sides are nearly parallel. 

 The teeth themselves are much larger, the roots of the pre- 

 molars and molars more distinct, and the hindermost molar 

 not so small relatively to the others, in some of the lowei 

 races, notably the Australians. 



