278 



THE DENTAL SYSTEM OF THE PRIMATES [SECT. A 



throughout the length of the slender jaws of the Odontoceti or 

 toothed whales. Moreover the reasonableness of this view seems 

 enhanced by the fact that many reptiles (and a reptilian stage is 

 postulated in the most widely-accepted view 1 as to the ancestry of 

 the Mammalia, cf. the scheme in Chapter ill. p. 37) possess such 

 simple teeth, which are often described as haplodont. Most 



Fig. 200. Molariform teeth of fossil reptile Diademodon. These teeth were im- 

 planted in sockets, and in their general appearance are mammalian. (After Osborn.) 



reptiles are also homodont, and it was from these, and not from 

 the rarer heterodont reptiles, that Cope traced the Descent of 

 Mammals (cf. Factors of Evolution, p. 331). It is noteworthy 

 that in many reptiles the teeth are ankylosed with the jaws, 

 whereas in mammals the teeth are thecodont ; they are implanted 

 in sockets, this being a form of articulation (not an ankylosis) 

 known as Gomphosis. The difference between mammals and 

 reptiles in this respect is not however absolute, for the Crocodilia 

 are thecodont, and so was the extinct reptile known as Diademodon. 

 (Cf. Fig. 200.) 



1 The fact must not be ignored that certain observations suggest a direct origin 

 of the Mammalia from the Amphibia, reptilian ancestors being thus omitted from 

 the direct line of descent. This view is losing ground at present. (Cf. footnote 4, 

 p. 279.) 



