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 ! 
The teeth are among the most 
important and the most variable 
organs of the vertebrate body. Long 
before the appearance of the osseous 
skeleton—~.e. among the lowest Ver- 
tebrates—teeth and tooth-like tegu- 
| \ mental scutes are found. We cannot 
IX 
: NN be far wrong in asserting that the 
Fic. 96.—-PaLataL Foups ov tHe acquisition of teeth by the Vertebrata 
SS 
N 
i 
1 
7 i 
s 1 
——e, Kok 
ESS v 
a EJ > \ 
(9 = , 
ff N ~ NYY 
; S = NWN | \ 
N 8 
NAN S ——— fon 
Nh) i \ _ > . =: aos 
\ \ N ” == nV ~ 
\\. K s 
\ < " S s , 
‘. QR C , 
SW. R Qe . " OSS 
\ \\, WS ~ = S 
BAA A\ \\ = 
i\\ \ \\ \\ 
\ Y PN. 
\ \\ 
ee ase sae ay: ng | Was & most important factor in the 
7r.p., palatal folds; p.y., papilla : 6 
Ed a pa struggle for existence. The size 
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 hfe, independently to acquire a similar dentition 
[as for example in the case of the Crocodilian (Gavialis) 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 Reptiles, 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. 
