430 



TEE DIGESTIVE APPARATUS IN MAMMALIA. 



They are worn more or less quickly, according to tlie kind of food the animal obtains, and 

 are sometimes broken in fighting. 



The molars are distributed in the two jaws, twelve being fixed in the upper and fourteen 

 in the lower. ' Nearly all of them are terminated by somewhat acute lobes, proper for tearing 

 animal food. The strongest in eacii jaw is, for the upper, the first back-molar or fourth in the 

 row, and iu the lower, the fifth. All in front of these are deciduous. 



After iheir complete eruption from the alveolar cavities, the Dog's teeth are no longer 



pushed outwards. They are remarkable 



Fig. 242. 



for their brilliant whiteness, which they 

 owe to the absence of cement on their 

 covering of enamel. 



The Cat has thirty teeth . twelve in- 

 cisors, four tusks, and fourteen molars, 

 eight of which are in the upper, and six 

 iu the lower jaw. 



All these teeth are constructed on the 

 same type as those of the Dog. The 

 canines are deeply striated on their ex- 

 ternal surface, instead of being smooth. 



Rabbit. — It may be noted that in the 



rabbit there are two incisors in the lower 



jaw, and four in the upper, two of which 



are placed behind the principal two. 



I I \\:^?^s\ # V There are ten molars in the lower, and 



\i \ \\ jl twelve iu the upper, which are, in prin- 



'l \ l\ ciple, as in the horse. 



H \ W /\ (The importance of a correct know- 



f \ (\ I I I le<ige of the period of eruption, shedding, 



* "^ ' ' replacing, and general wear of the teeth 



of the domesticated animals, as a guide 



to their age, induces me to give the table 



on p. 431 (from Leyh), as indicating at a 



glance the age at which the teeth appear, 



are shed, and replaced in the diflferent 



creatures. 



Baumeister divides the successive 

 evolutions in the wear of the tables of 

 the horse's incisor teeth into four periods 

 — from six years to extreme old age. 

 The first, the transversely oval period, 

 extends from six to twelve years; the 

 round, from twelve to eighteen years ; 

 the triangular, from eighteen to twenty- 

 four years, and tlie antero-postHrior oval or triangular, from twenty-four years and upwards. 

 Girard an.l other Frencii authorities shorten these periods somewhat. Tlie triangular period, 

 for instance, only lasts from fourteen to seventeen years.) 



Comparison of the Mouth op Man with that of Animals. 

 The shortness of Man's face influences the shape of the mouth ; therefore it is proportionately 

 shorter and wider than in the domesticated Mammals. 



1. Lips. — The lips have a thick, free, everted border. They are lined by a rosy mucous 

 membrane, which is insensibly continued inwanls by the buccal membrane. The upper lip 

 is limited by the nose and the naso-labial furrow ; the lower is limited by the mentodabial 

 groove. The first has in its middle the subnasal furrow. Their structure is analogous to those 

 of animals. 



2. C7/efi&«.— The cheeks are limited by the inferior border of the maxilla, the root of the 

 ear, the prominence of the chin, and the naso-labial furrow. Between the skin and the mucous 

 membrane, there is found — as in brutes— a glandular layer and muscles, chiefly the buccinator. 

 An adipose ball is always found near the anterior border of the masseter. 



dentition of the rabbit : THE TEETH SEEN FROM 

 THEIR TABLES. 



Upper jaw ; b, lower jaw. 



' Toussaint has observed that, in breeds with short faces, the molars decrease in number, 

 or are placed transversely, so as to find room in the maxillae. 



