OUR FACE FROM FISH TO MAN 



are infolded into the bases of the teeth. The 

 teeth succeed each other in an obHque series. 

 In Seymouria, a fossil reptile from the Permo- 

 Carboniferous of Texas, which is almost on the 

 borderline between the primitive amphibians and 

 all the higher levels of vertebrates, clear traces of 

 the labyrinthodont method of tooth-attachment 

 are still visible, but by the time of the higher 

 mammal-like reptiles all traces of the older method 

 had been lost and the teeth are set in sockets as in 

 the mammals, including man. 



ORIGIN OF THE MAMMALIAN PALATE 



No less important in determining the course of 

 future evolution in the mammals and in man were 

 the progressive changes in the palatal region 

 (Fig. 53). In the early amphibians the air taken 

 into the olfactory chamber was passed through 

 a pair of tubes opening by the choanse (Fig. 53 

 II, cho.) or internal nostrils, into the fore part of 

 the roof of the mouth, and from this point the 

 inspired air was practically swallowed, or forced 

 backward by the action of the throat muscles to 

 the opening of the windpipe. In the early mam- 

 mal-like reptiles (Fig. 53 V) the choanse opened 



118 



