72 DISEASES OF CATTLE, SHEEP, GOATS, ETC. 



mouth. This pad forms the gum and furnishes a bearing for the 

 incisors of the lower jaw. 



Sometimes, as in the horse, there are found supplementary mo- 

 lars, which, if four in number, will make up the whole to thirty-six, 

 though they are never all present at the same .time, as the supple- 

 mentary ones are shed before the molar dentition is completed. The 

 composition of the teeth of the ox is the same as those of the horse, 

 the only difference being in the arrangement of the several sub- 

 stances. 



Incisors. The incisors, eight in number, are placed like a key- 

 board at the extremity of a kind of rounded shoulder bone by which 

 the lower maxillary bone terminates; forming around the point a 

 perfect circle, when they have acquired their full development. In- 

 stead of being fixed in the alveoli, they possess a certain degree of 

 mobility, sometimes mistaken for a diseased condition. This is nec- 

 essary in order to prevent their wounding the cartilaginous pad of the 

 upper jaw, against which they press. 



They are divided, according to their position, into two centrals, 

 two first laterals, two second laterals, and two corner incisors. Each 

 incisor offers for consideration, two parts; one free, the other in- 

 cased, the root, and separated by a very marked constriction, the 

 neck. This arrangement gives to the tooth the form of a shovel, the 

 root representing the handle. 



The free portions of the incisors are flattened above and below, 

 and are thinnest and widest towards their anterior extremity, and 

 present two faces, an inferior or external, and a superior or internal ; 

 also three borders, an anterior and two lateral. The external face, 

 slightly convex, and of milk-white color, is covered with fine, undu- 

 lating striae, which disappear with age and leave the surface beauti- 

 fully polished. The internal face, flatter than the external, presents 

 in its middle a slight conical eminence, whose base widens and is ter- 

 minated near the free extremity of the tooth, while its sides are cir- 

 cumscribed towards each border by a well-defined groove. The two 

 lateral borders (the internal slightly convex in its length, the exter- 

 nal slightly concave in the same direction), make the free portion 

 appear as if it were thrown outwards. The anterior border is sharp 

 and slightly convex from one side to the other; it is the first part of 

 the tooth which is destroyed by wear. The root is rounded, slightly 

 conical, and implanted in the alveolus which is of the same form. In 

 youth, it shows at its extremity an opening communicating with an 

 internal cavity, analogous to that in the teeth of the horse, and 

 prolonged into the interior of the free portion. In the virgin tooth, 

 the enamel forms around the free portion a continuous layer, thin- 

 nest on the internal surface, and extending very scantily over a part 

 of the root. 



The dentine forms the remainder of the organ, and the (pulp) 

 cavity, which is originally a large space of the same form as the tooth, 

 is filled, as the animal grows old, by a new dentine, which, as in the 

 horse, has a yellower tint than the primitive ivory. When the ca,vit$ 



