TEKTH OF DIPHYODONTS. 295 



of large curved ever-growing incisors, in each jaw, is combined 

 with so many peculiarities of structure, as to have led to their 

 association into one order } called by Linnams Glires and by 

 Cuvier ' Rongeurs ' or ' Eroders,' from the gnawing power and 

 habit resulting from such dental modification. 



The incisors, fig. 235, i, i, are separated by a wide interval 

 from the molars : the upper pair, ib. *, describe a larger segment 

 of a smaller circle, the lower ones, ib. 'i, a smaller segment of a 

 larger circle ; these are the longest incisors, and usually have 



S3 5 



Dentition of the Capybuia. 



their alveoli extended below, or on the inner side of, those of the 

 molars, to the back part of the lower jaw, fig. 129 : but in the 

 Hare they reach only midway toward the angle. As in all teeth 

 of unlimited growth, the implanted part of the incisors, besides its 

 length, retains the form and size of the exposed part or crown, to 

 the widely open base, which contains a long conical persistent 

 dentinal pulp, ib. a, and is surrounded by the capsule in a pro- 

 gressive state of ossification, as it approaches the crown; an 

 enamel-pulp is attached to the inner side of that part of the cap- 

 sule which covers the convex surface of the curved incisor. 



The calcification of the dentinal pulp, the deposition of the 

 earthy salts in the cells of the enamel-pulp, and the ossification 

 of the capsule, proceed contemporaneously ; fresh materials being 

 added to the base of the vascular matrix as its several constituents 

 are progressively converted into the dental tissues in the more 

 advanced part of the socket. The tooth, thence projecting, 

 consists of a body of compact dentine, sometimes with a few short 

 medullary canals continued into it from the persistent pulp-cavity, 

 with a plate of enamel laid upon its anterior surface, and a 

 general investment of cement, which is very thin upon the enamel, 



1 Vol. ii. p. 276. 



