THE MOUTH. 



353 



in front of the true ones, and which may be four in number ; but these are 

 small teeth, having but little resemblance to the others, are most frequently 

 shed with the first deciduous molar, and are not replaced. 



" Generally considered, the molar arcades have not the same disposition 

 in both jaws. Wider apart in the superior one, they form a slight curve, 

 whose convexity is outwards. In the inferior jaw, on the contrary, the two 

 arcades separate in the form of a V towards the back of the mouth. Instead 

 of coming in contact by level surfaces, the molars meet by inclined planes, 

 and in such a way that the internal border is higher than the external 

 in the inferior molars, while the opposite takes place in the superior. 



" Like the incisors, each molar presents for study a free and a fixed 

 portion. 



" The free portion, nearly square in the upper molars, longer than wide 

 in the lower, shows at the external surface of the former two longitudinal 

 grooves, the anterior of which is the deepest, and which are continued on 

 the encased portion. This is not the case with the inferior molars, which 

 have but one narrow, and frequently an indistinct, groove. 



Fig. 160. 



PROFILE OP THE UPPER TEETH OF THE HORSE, MORE ESPECIALLY INTENDED TO 



SHOW THE MOLARS; THE FANGS HAVE BEEN EXPOSED. 

 a, Molar teeth ; 6, Supplementary molar ; c, Tusk ; d, Incisors. 



" The internal face in both jaws only shows one groove, and that but 

 little marked ; it is placed backwards in the upper molars, and is most 

 apparent towards the root. 



" The anterior and posterior faces are in contact with the corresponding 

 faces of the adjoining molars, except at the extremities of the arcades, where 

 the isolated face is converted into a narrow border. 



" With regard to the table of the tooth, it inclines, as we have already 

 mentioned, outwards in the lower jaw, and inwards in the upper ; a circum- 

 stance which prevents the lateral movements of the jaws taking place with- 

 out separation of the incisors, which separation removes them from friction." 

 In the virgin molar this face is completely covered with enamel, and 

 irregularly undulated. In it may be recognised the entrance to the two 

 infundibular openings, which are prolonged in the interior of the organ to 

 the extremity of the root, and which are almost entirely filled with cement 

 at the period when the tooth has completed its evolution ; they are only 

 vacant before the secretion of this crusta petrosa. In the tooth which has 



