430 



THE 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. , n . 



Tlie 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 btvongest in each jaw is, for the upper, the first back-molar or fourth in the 

 row, and in 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 whitenesa, 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 whicli are in the upper, and six 

 in 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 tiie upper, two of which 

 are placed behind the principal two. 

 There are ten molars in the lower, and 

 twelve in the upper, which are, in prin- 

 ciple, as in the horse. 



(The importance of a correct know- 

 ledge of the period of eruption, shedding, 

 replacing, and general wear of the teeth 

 of tlie 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 different 

 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-posterior oval or triangular, from twenty-four years and upwards. 



Girard an.l other French authorities shorteti these periods somewhat. The triangular period, 



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



COMPAUISON OF THE MOUTH OF MaN WITH THAT OF AnIMALS. 



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

 shorter and widei' 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 inwards by tlie buccal membrane. The upper lip 

 is limited by the no.'^e and the ufiso-labial furrow; th.- lower is limited by the mento-labial 

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

 of animals. 



2. CheeJis.—'n\Q 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. 



a, Upper jaw ; h, lower jaw. 



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

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



