382 ZOOLOGY. 
the palate and two rows of comb-like teeth on the tongue. 
In the lamprey the edges of the circular mouth are provided 
with circular rows of conical horny teeth. The teeth of 
higher Vertebrates are derived from the cells of the mucous 
membrane of the mouth, which is formed of connective tis- 
sue as well as epithelium. The teeth of fishes are developed 
not only in one or several rows in the lip, but may also arm 
the bony projections into the mouth-cavity of the palate, 
vomer and parasphenoid bones and the hyoid and bran- 
chial arches. In the Amphibia teeth survive on the palatine 
and vomerine bones, more rarely on the parasphenoid ; among 
the reptiles, the snakes and lizards alone have teeth on the 
palatine and pterygoid bones, while in the crocodiles and in 
mammals the teeth are confined to the maxillary bones. In 
the geckos, snakes and the crocodiles, as well as the mam- 
mals, the teeth are inserted in sockets (alveoli) of the jaw. 
(Gegenbaur. ) 
In certain extinct birds (Odontornithes) there were teeth 
in the jaws, though all existing birds are toothless. It is 
said that rudimentary 
teeth were found by 
Geoffroy St. Hilaire in 
the jaws of a parrot. 
Blanchard afterwards 
found the germs of 
teeth there, though 
they never come 
through. Inthe Mam- 
mals the teeth are dif- 
Fig, 383.—Teeth of the Tasmanian devil. The ferentiated into inci- 
isors are situated in front of the large conical 3 . 
Sie teeth. 2,3, premolars; m, 1-4, four molar sors, Canines, premo- 
seeth, Aten Diten lars and molars (Fig. 
383). In descriptive anatomy the teeth are for convenience 
expressed by a formula, the number of teeth of the upper 
jaws being placed like the numerator of a fraction, and those 
of the lower jaw like the denominator, the initials of the 
names of the teeth being placed before the figures, thus 
2-9 ~1=1. 483 3-3 
poss pe le. 
9—2’ 1-1’ 2-2 3-8 
the dental formula of man is J 
