170 MAMMALIAN DENTITION 



proximation of the nose and chin, the hollowness of the cheeks 

 and temples from wasting of the muscles, the loss of angularity 

 in the skull and the thin tapering neck are apparent in life. 

 Precisely the opposite is noted during adolescence as the milk 

 dentition becomes replaced by the occluding permanent set. 

 Certain local features such as the increase in size of the alveolar 

 portions of the jaws are the direct result of the development 

 of teeth but the permanent dentition must be present in occlu- 

 sion before the full complement of secondary masticatory 



Fig. 59. — Skull of young Gorilla superposed upon that of an adult animal. (After 

 Keith.) Note that .with the appearance of the permanent teeth the temporal and 

 occipital muscles grow so large that additional crests are formed upon the skull for 

 their accommodation and attachment. 



features appears. In Fig. 58 Ave have reproduced the char- 

 acteristics of the mandible at different periods of life. To 

 render more clearly the changes which the skull undergoes 

 during adolescence reference should be made to Fig. 59 which 

 represents the skull of an infant Gorilla superposed upon that 

 of an adult. This illustration serves to indicate the changes 

 brought about indirectly through the functional use of the 

 teeth. 



After this digression Ave return to the discussion of those 



