380 



ANATOMY OF VERTEBRATES. 



exposed by a vertical section through the middle of two of 

 the 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 series of minute cells and 

 inosculating loops at the line of junction with the enamel. 

 This substance, fig. 262, e, is as thick as the dentine, and 

 consists of a similar combination 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 



262 



Two of the upper phuryngeal teeth i Scaras -, nuign. r. 



stand at right angles, and, having proceeded parallel to each other 

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

 divide, the branches crossing each other obliquely, and finally 

 terminating in the cellular boundary between the enamel and 

 dentine. 



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

 from the ossification of the capsule is first removed from the apex 

 of the tooth, then the enamel constituting that apex, next the 

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

 the hollow tooth : and thus is produced a triturating surface of 

 four substances of different degrees of density. The enamel, 



