lOO 



OUTLINES OF NATURAL HISTORY. 



limbs. The skull (fig. 45) is a strong bony box or case 

 within which that most important organ, the brain, is 

 protected. 



Besides the true brain-case, however, the skull also 



y 





Kg- 45.— Skull of the Sheep-Uog. I Lower jaw ; hj Back teeth or molars; 

 c Eye-teeth or canines; % Front teeth or incisors. 



consists of the bones of the face, and likewise serves for 

 the protection of the organs of vision and hearing. The 

 bones of the face are much lengthened out, so as to form 

 a regular muzzle, at the end of which the mouth opens. 

 The lower jaw (/) is composed of two halves, each consist- 

 ing of a single piece, and it is jointed to the skull behind, 

 directly, and not by means of any "quadrate bone," such 

 as exists in Eeptiles and Birds. Both jaws are armed 

 with teeth, which are sunk in distinct sockets in the bony 

 substance of the jaw. In the front of each jaw are placed 

 six teeth, the so-called front teeth or "incisors" (Latin, 

 incido, I cut into), which have sharp cutting-edges, and 

 are used in dividing the food (fig. 45, ^). On each side 

 of these are situated the so-called eye-teeth or " canine 

 teeth" (Latin, canis, a dog), two in each jaw, and there- 

 fore four in number altogether. The canine teeth (fig. 45, 



