RUMINANTS. 537 



but the first, which is placed further in advance of the molar series, is 

 retained in the form of a small subcompressed, recurved, trenchant and 

 sharp-pointed canine, implanted by a single root : the second premolar 

 in the lower jaw is usually soon shed, the premolars are here indicated 

 by numbers according to their appearance as functional teeth. 



In the ordinary Ruminants, the upper premolars are implanted 

 by three fangs, two outer and one inner : the upper true molars 

 by four fangs, two outer and two inner. In the lower jaw both 

 premolars and molars are implanted by two fangs, but the second 

 fang in the last molar is very thick and consists of two connate fangs 

 (PI. 133, fig. 1). The crowns extend some way into the sockets 

 before dividing into fangs ; but these are always formed sooner than 

 in the Horse, and increase in length with the age of the Ruminant. 



193. Microscopic Structure. — In the true vegetable-feed^ing hoofed 

 Mammalia, as in the small Rodents with a similar regimen, the crowns 

 of the molar teeth are complicated by the interblending of layers of 

 enamel and cement with the dentine or basal substance of the tooth : 

 the microscopic structure of the several tissues does not essentially 

 vary from that of the same tissues in the more simple teeth of the 

 Mammalia ; except that in the dentine of the incisors a few vascular 

 canals are retained, and that the cement of the molars, being of great 

 thickness, also presents vascular canals in addition to the minuter 

 radiated cells. The calcigerous tubes of the dentine in the incisor of a 

 Deer, maintain their parallelism best and are least bent, in the last half 

 or third of their course, i. e. nearest the enamel; and fall into stronger 

 and less regular curves as they approach the pulp-cavity, altering 

 their curves somewhat abruptly, and along contour-lines indicated 

 by the change of curve and by the numerous minor branches there 

 given ofi', most of which communicate with or dilate into minute 

 cells which likewise add to the distinctness of the contour lines. 

 The dentinal tubes are most curved at their commencement from, 

 or rather termination in the pulp-cavity, where in the incisor of the 

 Red Deer, they present a diameter of ii^th of an inch, and are 

 separated by interspaces of about g^^uth of an inch in width. They 

 soon begin to divide dichotomously into primary branches, and then 

 to send off" numerous fine ramuli whereby the more parallel and 

 straighter continuations of the main tubes which form the peri- 



