404 



PRACTICAL ZOOLOGY 



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principal glands are the salivary glands connected with the 

 mouth, and the liver and pancreas connected with the small 



intestine. These glands 

 secrete digestive juices, 

 and other smaller glands 

 in the walls of the 

 stomach and intestine 

 share in this duty. 



Teeth. — The teeth 

 of mammals are among 

 their most interesting 

 possessions since they 

 vary so much in the 

 different species and in- 

 dicate what kind of 

 food is eaten by their 

 owners. Most mam- 

 mals are provided with 

 teeth, but the whale- 

 bone whales, the egg- 

 laying species, and ant- 

 eaters are without them 

 in the adult stage, and 

 in some forms they have 

 never been found, even 

 in the embryo. 



The teeth are em- 

 bedded in sockets in 

 the bone, and arise from 

 the mucous membrane 

 of the mouth. The 

 principal forms of teeth 

 and the relations of the 

 materials composing 

 them are shown in Fig- 



Fig. 275. — Diagrammatic section 

 forms of teeth. 



I, incisor or tusk of elephant with pulp cav- 

 ity open at base ; II, human incisor, during de- 

 velopment, with pulp cavity open at base ; III. 

 completely formed human incisor, opening of 

 pulp cavity small ; IV, human molar with broad 

 crown and two roots; V, molar of ox, enamel 

 deeply folded and depressions filled with cement. 



Enamel, black; pulp, white; dentine, hori- 

 zontal lines; cement, dots. (From Flower and 

 Lydekker.) 



