BEASTS OF THE FIELD 



21 



peculiar pointed crowns known as the " pre-molars," and two 

 much larger " molars." These pre-molars and molars form the 

 " cheek-teeth." Their work is to chew up the food torn off by 

 the cutting teeth. The study of the different forms of teeth 



c<t 



FIG. 4. Section of the skull of a dog showing the different forms of the teeth, the 

 general features of the skull, z, incisors ; c, canines ;pm, pre-molars ; m, molars 

 the pre-molars and molars form the " cheek-teeth " ; cd, condyle of lower jaw for 

 attachment to the skull ; c0, condyle of skull for articulation with spinal column ; 

 so, supra-occipital bone ; pa, parietal bone ; fr, frontal bone ; , bones of middle 

 or internal ear ; j, septum of nose ; /, " turbinals," the skeleton which supports 

 the mucous membrane of the nose bearing nerves of scent, etc. 



and their uses is one of the greatest interest, and something 

 on this head will be found later in these chapters. 



At the time of birth mammals are toothless. Very soon, 

 however, teeth make their appearance, and these as a rule 

 are shed, and replaced by a permanent set. Because the first 

 set appear during the time that the animal is being fed upon 

 milk they are known as the " milk-teeth." 



The backbone, or spinal column, as may be seen in the outline 

 drawing (p. 33), is made up of a series of separate bones having a 

 more or less barrel-shaped body, and supporting an arch of bone 

 (Fig. 5). In the living animal these barrel-shaped pieces form 

 a long more or less curved rod, and their separate arches form 

 a tube through which runs the spinal cord, the great nerve 

 supply, from which run the nerves which control the movements 

 of the body and limbs, and convey the sensations. 



