652 



UNGULATES. 



that it undergoes a change of tissue : " Whilst it yielded enamel 

 only it was thin and transparent, to give cement it becomes thick, 

 spongy, and of a reddish colour."(l) The obvious characters of the 

 enamel organ and cement-forming capsule, are here correctly defined ; 

 but the one instead of being converted into the other, is, in fact, 

 changed into its supposed transudation : the enamel fibres being 

 formed, and properly disposed in the direction in which their chief 

 strength is to lie, by the assimilative properties of the pre-arranged 

 elongated prismatic non-nucleated cells of the enamel pulp, which 

 take from the surrounding plasma the required salts and compact 

 them in their interior. 



Whilst this process is on foot, and before the enamel-fibres 

 are firm in their position, the capsule begins to undergo that 

 change which results in the formation of the thick cement: the 

 calcifying process commences from several points, and proceeds 

 centrifugally, radiating therefrom, and differing from the ossifica- 

 tion of bone chiefly in the number of these centres, which, 

 though close to the new-formed enamel, are actually in the substance 

 of the inner vascular surface of the capsular folds. The cells arrange 

 themselves in concentric layers around the vessels, and act like 

 those of the enamel pulp in receiving into their interior the bone- salts 

 in a clear and compact state ; during this process they become 

 confluent with each other, their primitive distinctness being indicated 

 only by their persistent granular nuclei, which now form the radiated 

 Purkingian corpuscles. The interspaces of the concentric series of 

 confluent cells become filled with the calcareous salts in a rather 

 more opake state, and the conversion of the capsule into cement 

 proceeds according to the processes more particularly described 

 in the Introduction, until a continuous stratum is formed in close 

 connection with the layer of enamel. 



The uncalcitied part of the capsule, always much softer than 

 cartilage, is very readily detached from the calcified part, and to 



(1) "Seulement elle change de tissu: tant qu'elle ne donnait que de I'email, elle etait 

 mince et transparente ; pour donner du cortical elle devient cpaisse, spongieuse, opaque et 

 rougeatre." — Annales du Museum, torn, viii, p. 99. ' Ossemens Fossiles,' Ed. 1834, 8vo. 

 torn. I, p. 514 



