314 STRUCTURE OF THE SHEEP. 



followincr year by those adjoining, so that by five years the 

 whole eight teeth are thus renewed, and the sheep is then 

 said to be full-mouthed. Although the order and period of 

 these changes are sufficiently regular to ensure them as a suffi- 

 cient criterion for a general rule, yet it is not without exception, 

 as sometimes the permanent teeth appear much earlier, and 

 at others their appearance has been protracted to a later 

 period. 



After the sheep becomes full-mouthed, there is no method 

 of judging of the age with accuracy, but the teeth rarely 

 remain perfect long, particularly if fed on turnips ; some of 

 them are lost or become broken, and the sheep is then said 

 to be broken-mouthed. 



The incisor teeth are somewhat conical in shape, the point 

 being inserted in deep sockets ; the portion visible is covered 

 by a very hard transparent material called the enamel, and 

 it is brought to a sharp edge at the anterior part, so that it 

 cuts very much like a chisel. Compared with those of the 

 horse the incisor teeth appear somewhat loose, but this is 

 rather an advantage than otherwise. The food, being em- 

 braced between the incisor teeth and the pad above, is torn 

 asunder by the nodding action of the head, and the food is 

 conveyed by the tongue to the molars or grinders. When 

 turnips, however, form the diet, the food is scooped out, as 

 it were, by the teeth alone, and they are consequently sooner 

 worn out and broken ; but even otherwise, this effect gener- 

 ally follows a few years after the mouth becomes perfect. 

 The molar teeth are six in number, on each side of each jaw ; 

 they are firmly planted in deep sockets, and their faces are 

 covered with enamel. These faces are very irregular, but 

 admirably adapted for tearing and grinding the tough and 

 unyielding grass ; and they are also secured in their positions 

 by means of the gums, which, in common with the other 

 parts of the mouth, are covered with a mucous membrane, 

 and in some parts a firm dense material is interposed between 

 the mucous membrane and the bone. 



The sides of the mouth are formed by the cheeks, which 

 are composed of skin and membrane sufficiently loose to 

 admit the limited motion of the jaws ; they are connected 

 with the powerful masseter muscles, which form the greater 

 part of the bulk of the face, and principally occasion the 

 grinding motion of the jaws. In the skull we find the lower 

 jaw considerably narrower than the upper, but in the living 



