156 



THE STRUCTURE OF MAN 



as are still found among the lower Mammals in the form of 

 horny teeth or ridges (Ornithorhynchus, certain Marsupials, and 

 Edentates). 



The extreme anterior border of the palate bears a median 

 eminence, the papilla palatina (p.p., 

 Figs. 95, 96). On either side of 

 this and of the raphe the naso- 

 palatine canal, already described 

 (ante, p. 146), opens. 



TEETH l 



The teeth are among the most 

 important and the most variable 

 organs of the vertebrate body. Long 

 before the appearance of the osseous 

 skeleton i.e. among the lowest Ver- 

 tebrates teeth and tooth-like tegu- 

 mental scutes are found. We cannot 

 be far wrong in asserting that the 



FIG. 96. PALATAL FOLDS OF THE acquisition of teeth by the Vertebra ta 

 RACOON (Procyon lotor}. was a mos t important factor in the 



and form of the teeth are greatly 

 determined by adaptation to the various conditions of life. 

 It is therefore often difficult to decide whether similar tooth 

 forms in fossil animals are cases of analogy or of homology. It 

 is quite possible for different races of animals, in adaptation to 

 similar modes of life, independently to acquire a similar dentition 

 [as for example in the case of the Crocodilian (Gamalis) and the 

 Dolphin (Platanista) living side by side in the Ganges]. If, 

 among the lower Vertebrata, we set aside dental ridges resulting 

 from the fusion of several distinct teeth, and the compound teeth 

 of many Fish, the teeth, as far up as the lower Eeptiles, are, for 

 the most part, simple pointed cones. In these animals they serve 

 only for seizing the prey, the further disintegration of which 

 takes place in the stomach and intestine. In the Mammalia 

 the food is more or less triturated in the mouth, and that chiefly 

 by the cheek teeth. 



The dentition of the Primates is, as compared with that of 



1 In this account of the teeth the researches of Rose have been largely 

 followed. 



, papilla 



