THE RABBIT 439 



of the mouth, but with a free tip in front. It bears 

 papillae of several kinds which subserve the sense of 

 taste. The teeth differ from those of the dogfish and frog 

 in that (1) they are not all alike, (2) they are inserted in 

 sockets in the jaw, whereas those of the dogfish are 

 embedded in the skin and those of the frog are fused to 

 the jaw, (3) they are borne on the edges of the jaws only, 

 and not on the roof of the mouth like the vomerine teeth 

 of the frog, (4) instead of being continually replaced by 

 the upgrowth of the skin from a groove as in the dogfish, or 

 one by one as in the frog, they are in two definite sets, the 

 milk teeth and the permanent teeth, of which the first is lost at 

 an early age and replaced for life by the second. The 

 teeth do not form a continuous series as in man, but the 

 front teeth are separated from the grinding teeth by a wide 

 gap or diastema, in the position in which the canine or 

 dog teeth should stand, these teeth, with others, being 

 absent from the rabbit. In the upper jaw the front teeth 

 or incisors number two pairs, the first pair being long, 

 curved, and chisel-shaped, and the second , pair small and 

 hidden behind the first. Unlike the rest of the teeth, and 

 unlike the front teeth of most animals, the incisors of the 

 rabbit do not cease to grow when they have reached a 

 certain size, but continue to add to their bases as fast as 

 they are ground down at the top. The six pairs of 

 grinding teeth are all much alike in appearance, having 

 broad, ridged tops, but they are divided into two sets by 

 the fact that the first three, known as premolars, are 

 preceded by milk teeth, while the last three, known as 

 molars, are not. In the lower jaw there is only one pair of 

 incisors, these being shaped like the first pair above, 

 with which they work in gnawing off the food which is 

 munched fine by the grinders. There are two pairs of 

 premolars and three pairs of molars. It is usual to express 

 the number and arrangement of the teeth of mammals by 

 a dental formula. Thus, in the pig, which has a typical set 



of teeth, the formula is i±c- pm - m 2., giving 22 on 



3 x 4 3. 

 each side of the mouth, or 44 in all. With this we may com- 

 pare the dentition of the rabbit, which is i - c - pm ^ m ^. 



1023, 



