HI MAMMALIAN SKULLS 10o 



tory angle " and " occipital angle " become more 

 obtuse; and that the " cranio-facial angle," be- 

 comes more acute by the bending down, as it 

 were, of the facial axis upon the cranial axis. At 

 the same time, the roof of the cranium becomes 

 more and more arched, to allow of the increasing 

 height of the cerebral hemispheres, which is 

 eminently characteristic of man, as well as of that 

 backward extension, beyond the cerebellum, which 

 reaches its maximum in the South American Mon- 

 keys. So that, at last, in the human skull (Fig. 

 30), the cerebral length is between twice and 

 thrice as great as the length of the basicranial 

 axis ; the olfactory plane is 20 or 30 on the under 

 side of that axis ; the occipital angle, instead of 

 being less than 90, is as much as 150 or 160 ; the 

 cranio-facial angle may be 90 or less, and ' the 

 vertical height of the skull may have a large 

 proportion to its length. 



It will be obvious, from an inspection of the 

 liagrams, that the basicranial axis is, in the 

 ascending series of Mammalia, a relatively fixed 

 ine, on which the bones of the sides and roof of 

 :he cranial cavity, and of the face, may be said to 

 -evolve downwards and forwards or backwards, 

 tccording to their position. The arc described by 

 my one bone or plane, however, is not by any 

 neans always in proportion to the arc described 

 >y another. 

 Now comes the important question, can we 



