380 



ANATOMY OF VERTEBRATES. 



exposed by a vertical section through the middle of two of 

 tlio superior denticles. Each tube is minutely undulated: 

 it dichotomises three or four times near its termination, sends 

 off many fine lateral branches into the clear uniting sub- 

 stance, and finally terminates in a scries of minute cells and 

 inosculating loops at the line of junction with the enamel. 

 This substance, fig. 202, e, is as thick as the dentine, and 

 consists of a similar comljination of minute tubes and a clear 

 connecting substance. The tubes may be described as com- 

 mencing from the peripheral surface of the tooth to which they 



stand at right angles, and, having ]n'oceedcd parallel to each otlier 

 Iialfway towards the dentine, they then begin to divide and sub- 

 divide, tlie branches crossing each other obliquely, and finally 

 terminating in the cellular boundary between the enamel and 

 dentine. 



In the progress of attrition, tlie thin coat of cement resulting 

 from the ossification of the capsule is first removed i'rom tlic apex 

 of the tootli, tlien (lie enamel constituting tliat a])ex, next the 

 dentine, and, finally, the coarse central ccllnlar bone, supporting 

 tlic holliiw tddth : and thus is jiroduced a triturating surface of 

 foiu- sul)s(ances oi' dillerent derives cif dciisitv. 'I'lie enamel. 



