OUR FACE FROM FISH TO MAN 



to the essentially mammal-like dentition of the 

 cynodonts (Fig. 50 VI), in which the adult denti- 

 tion, as in man and other mammals, consists of 

 incisors, canines, premolars and molars, and in 

 which the dentition was apparently reduced to 

 two sets corresponding to our milk and permanent 

 teeth. Moreover, each tooth in the cynodonts 

 was set in a distinct socket as in the mammals. 

 Hence these reptiles had already traveled far on 

 the long road from fish to man. 



We have followed some of the progressive 

 changes in the jaws of these forms, in which the 

 dentary bone finally became the predominant 

 element and gained contact with the squamosal 

 bone of the skull (Fig. 21), while the bones behind 

 the dentary were reduced to slender proportions 

 (Fig. 52). These changes, however they may 

 have been initiated, were obviously associated 

 with a great development of the temporal, masseter 

 and pterygoid muscles of the jaws (Fig. 61), 

 which have very strongly braced areas of origin 

 and attachment. To the activity of the temporal 

 muscle we apparently owe the first appearance of 

 the temporal fossa (Fig. 48 IV) in the shell of bone 



that formerly roofed over the jaw muscles, while 



116 



