1877.] 



Mr. C. S. Tomes on Vascular Dentine. 



45 



be withdrawn from a tooth which is advancing in calcification into osteo- 

 dentin, because it is permeated through and through by a network of 

 calcifying trabecular 



It is possible by careful observation to distinguish in sections of dried 

 teeth true vaso-dentine from osteo-dentine ; the majority of teeth consist- 

 ing of the latter tissue ordinarily pass as consisting of the former (e. g. 

 the teeth of the pike, of many Plagiostomi, which really consist of osteo- 

 dentine, but are always described as vaso-dentine). 



The teeth of the hake are selected as an illustration of vaso-dentine ; 

 they have large pulps, richly vascular, and red blood circulates abundantly 

 through the capillary channels of the dentine, so that the tooth, when 

 the fish is alive, is brilliantly red. 



The matrix of the dentine is dense and solid ; i. e. it is not permeated 

 by dentinal tubes. 



The transition between typical vaso-dentine, such as that of the 

 Gradidse, and hard unvascular dentine, such as that of most mammalian 

 teeth, is gradual. 



Thus most of the Pleuronectidse have teeth which at their basal halves 

 consist of typical vaso-dentine without dentinal tubes, just like that of 

 the GadidaD ; but above the middle, dentinal tubes radiating out from the 

 central pulp-chamber begin to appear, at first sparsely, and the capillary 

 canals to become fewer, till the apex of the tooth consists of ordinary 

 fine-tubed dentine, in which few, if any, capillary channels exist. 



And in Serrasalmo there are teeth which are throughout composed of a 

 dentine permeated by dentinal tubes, but in the basal half of the tooth a 

 few capillary channels are present. Prom such a form of dentine to 

 ordinary hard unvascular dentine is but a short step. 



The development of osteo-dentine is illustrated by a description of the 

 teeth of a pike ; the outer layer is developed, like dentine, from a layer 

 of cells analogous to, though less specialized than, odontoblasts ; and so 

 soon as this has been calcified the interior of the tooth is formed by a 

 rapid ossification, just as the subjacent bone is formed. 



Vaso-dentine therefore differs much less from true or unvascular 

 dentine than osteo-dentine does, the relation between the three tissues 

 being well seen in the teeth of Sparidse. 



In Sargus ovis the incisor-like front teeth appear to be implanted by long 

 roots ; these are formed by the dentinal formative pulps, just as are the 

 roots of ordinary rooted teeth. 



But there is this peculiarity in the nature of the process : the dentinal 

 pulp, so long as the " crown " (or portion which will be above the bone) is 

 being developed, is converted into fine-tubed unvascular dentine ; but so 

 soon as the root or implanted portion commences to be formed, this 

 same dentinal pulp, the apex of which is even yet forming unvascular 

 dentine, calcifies into vaso-dentine. Without there being any exact 

 break or breach of continuity, the change from true dentine to vaso- 



