DEVELOPMENT. 17 



condensed into concentric layers, which then become, as they are 

 successively impregnated with the calcareous salts, the walls of the 

 medullary canals. (1) 



In the shark, and all those fishes in which the teeth are completely 

 formed without going beyond the papillary stage of development, there 

 is no distinct enamel- pulp ; the dense exterior layer of the tooth is 

 formed by the calcification of the ' membrana propria' of the pulp, 

 which, therefore, precedes the formation of the ordinary dentine. But 

 in the file-fish fBalistesJ, the sargus, the gilt-head fChrysophrysJ , and 

 some other fishes, a conspicuous enamel-pulp is developed from the 

 inner surface of the capsule which surrounds the bone-pulp : this enamel 

 organ terminates, as in the human subject, before the capsule is re- 

 flected upon the base of the pulp. It has a firmer tissue, more 

 closely resembling that of the ordinary pulp, than in the mammalia : 

 and, when examined under the microscope, presents numerous and 

 close-set fine fibres near that surface which is next the bone-pulp, 

 and to which these fibres are generally placed at right angles. The 

 base of the enamel organ, which is attached to the capsule, presents 

 a granular and fibrous tissue blended together. I have not been able 

 to trace any capillaries from the capsule into the substance of the 



(1) In those fishes, and they include the greatest part of the class, in which the teeth are at- 

 tached by anchylosis to the jaws, the mode in which the calcareous particles are deposited in the 

 gelatinous frame-work or pulp is modified as the calcification approaches more or less gradually 

 towards the base of the tooth, until at length the pattern or texture of the calcified pulp cannot 

 be distinguished from that of the bone with which it thus becomes continuous. It is not with- 

 out interest to observe how Cuvier, who had clearly detected this actual ossification of the base 

 of the pulp in the teeth of many fishes and reptiles, should have conceived it to be a process so 

 distinct from that peculiar to the supposed inorganic tooth, that he felt himself called upon to 

 correct the error he had fallen into in stating, in his " Le9on8 d'Anatomie Comparee," this 

 ossified base of the anchyloaed tooth to be its root. Describing the teeth of lizards, in his " Osse- 

 mens Fossiles," tom. V, 2e partie, p. 274, Cuvier says : — " Cette base ne se divise point 

 en racines ; mais quand la dent a pris son accroissement, il arrive le meme phenomene que 

 dans les poissons. Le noyau gelatineux s'ossifie ; il s'unit intimement d'une part, a I'os 

 de la machoire, en contractant, de I'autre, une adherence intime avec la dent qu'il a 

 exsudee. — J'avais deja expose I'histoire de cette dentition dans mes Lemons d'Anatomie 

 Comparee, III. iii. 113, etc.; mais j'y ai aussicommis I'erreur d'appeler racin" cette partie cellu- 

 leuse et osseuse qui s'unit a I'os maxillaire." The application of the microscope to the investiga- 

 tion of the structure of the teeth has brought to light many instances in which the croivn of 

 the tooth ought, for the same reasons, to have as little title to be considered a part of the tooth 

 as the root. 



