170 



THE SHEPHERD'S MAKUAL. 



and especially of those which are armed with heavy horns. The 

 skull consists of two tables or pl-ites, half an inch or more apart, 

 the outer thick and tough, the inner hard and brittle. These 

 plates are connected by ridges of bone, which divide the space 

 between them into compartments called sinuses. This structure 

 gives the skull exceeding strength and ability to resist blows and 

 punctures by sharp substances. The bones of the head are joined 

 together by sutures or dove-tails, which are also conducive to ex- 

 treme strength. In this manner the brain is protected, and the 

 horns are provided with a solid and elastic foundation. The form 

 of the head is shown in figure 61, in which 1 is the occipital bone ; 

 2, parietal bone ; 3, core of right frontal 

 bone; 4, the left core covered by its horn ; 

 5, superciliary foramen ; 5 1 , channel des- 

 cending from it ; 6, lachrymal bones ; 7, 

 zygoma ; 8, nasal bones ; 9, supermaxili- 

 ary bones ; 10, premaxiliary bones ; 10 1 , 

 its internal process; 11, incisive opening. 

 The cavity which contains the brain is 

 less than a third the size of the rest of the 

 skull, the larger portion being devoted to 

 the functions of eating and smelling. 

 The space devoted to mastication is large, 

 an"! the space oicupied by the nostrils, 

 which are the breathing passages, rela- 

 tively small. Most of the bones of the 

 face are hollow, and are divided into sev- 

 eral sinuses and cells by which the head is rendered light and 

 strong. The sinuses and cells are lined with membranes which 

 secrete mucus, and are therefore called mucous membranes. The 

 inner cavity of the skull is lined with several membranes which 

 still further add to its strength, and to the security of the brain. 

 The teeth of the sheep consist of incisors or cutters, and molars or 

 grinders. There are 8 of the former, all being upon the lower jaw, 

 and 24 of the latter. Upon the upper jaw, in place of cutting 

 teeth, the sheep has, in common with most of the ruminants, a 

 cartilaginous plate or cushion, upon which the teeth of the lower 

 jaw impinge when the mouth is closed. The sheep has no canine 

 teeth or tusks. There is a long space of the jaws on each side be- 

 tween the incisors and molars, which is destitute of teeth. The 

 milk teeth, or deciduous or temporary teeth of the sheep, are 

 twenty in number; the eight incisors on the lower jaw, and three 

 molar teeth on each side of both jaws or twelve in all. The two 



Fig. 61. BONES OF A 



KAM'S HEAD. 



