68 COMPARATIVE ZOOLOGY. 



they are planted also in the roof of the month. With 

 few exceptions, they are conical and curved (Fig. 33). In 

 the Serpents they are longest and sharpest; and the ven- 

 omous species have two or more fangs in the upper jaw. 

 " ' " These fangs contain a canal, 



fe^ijjl^j^^^^^fe^ through which the poison 



'^^S^V^^^^pp^^P^^!^ is forced by muscles which 



/ ^^S ^^^il^ ^^v^ compress the gland. The 



^^^^^^^-S-j^^^ bones to which they are at- 



'• tached are movable, and the 



Fig. 33.— Poison Appnrntns of the Hattie- fangs Ordinarily lie flat upon 



enake; gr, glaud, with duct, leading to ,i r *. i -i j. 



the fang,/; m, elevator muscles of the tlie gUmS, but are brought 



jaw, which,in contracting, compress the j^j vertical pOSition in 



gland ; 8, salivary glands ou the edge of i 



the Jaws : n, nostril. the act of Striking. As a 



rule, the teeth of Eeptiles are simply soldered to the bone 

 ■which snppoi'ts them, or lodged in a groove; but those of 

 Crocodiles aj-e set in sockets. Keptilian teeth are made 

 of dentine and a thin layer of cement, to which is added 

 in most Saurians a coat of enamel on the crown. 



In the majority of Mammals, the teeth are limited in 

 number and definite in their forms. The number ranges 

 from 1 in the Narwhal (but the longest tooth in the king- 

 dom) to 220 in the Dolphin. The average is 32, occur- 

 ring in Euminants, Apes, and Man; but 44 (as in the 

 Hog and Mole) is called the typical or normal number, 

 and this number is exceeded only in the lower groups. 

 When very numerous, the teeth are of the Keptilian type, 

 siuall, pointed, and of nearly equal size, as in the Porpoise. 

 In the higher Mammals, the teeth are comparatively few, 

 and differ so much in size, shape, and use, that they can 

 be classed into incisors, canines, premolars, and molars. 

 Such a dental series exhibits a double purpose, prehension 

 and mastication. The chisel-shaped front teeth are fitted 

 for cutting the food, and hence called indsors. These 

 vary in number : the Lion has six in each jaw ; the Squir 



