496 THE ANATOMY OF VEKTEBEATED ANIMALS. 



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 backwards or forwards upon this 

 axis. The position and the aspect of the occipital foramen 

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

 squama occipitis which lies above the superior semicii'cular 

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

 ment, 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 pre- 

 maxilla 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 prognathons ; when it 

 is small, the face is ortliognatlious. This is the fundamental 

 condition of prognatliism or ortliognatliism. A secondary 

 condition is the form of the alveolar poi-tion of the upper 

 jaw, which, so far as it is vertical, tends towards ortho- 

 gnathism ; 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, vsdde and evenly rounded ; while, in the most 

 prognathous, it is prolonged, and its sides are neai-ly 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 lower 

 races, notably the Australians. 



The mental prominence may project beyond the line of 

 the vertical alveolar margin of the mandible, in the higher 

 races, or it may be almost obsolete, and the alveolar margin 

 may be greatly inclined forwards, in the lower. 



The different races of mankind are divisible into two 

 primary divisions ; the JJlotrichi, vrith crisp or woolly hair, 

 and the Leiotrichi, with smooth hair. 



