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Mr. C. S. Tomes on Vascular Dentine. 



[Mar. 8, 



Vaso-denthste is the term generally used to designate a variety of 

 dentine exceedingly common in the class of Fish, in which the substance 

 of the tooth is permeated by a number of anastomosing tubes, of con- 

 siderable size, which have been called "medullary" canals, as they have been 

 supposed to contain pulp-tissue ; whilst osteo-dentijn'e is used to desig- 

 nate that variety of vaso-dentine in which the matrix is arranged in con- 

 centric layers round the canals, like the laminar of an Haversian system 

 in bone, and in which spaces like the lacunae of bone occur. 



The author would not propose to introduce any new terms, but to 

 render more precise and definite the meaning attached to the terms 

 vaso-dentine and osteo-dentine, premising that the application of the 

 two words will be greatly altered by so doing. 



The author defines yaso-deisttiiste as a modification of dentine which 

 is permeated by a system of canals far larger than ordinary dentinal 

 tubes, which anastomose freely with one another, and contain capillary 

 blood-vessels and nothing else. That is to say, each several canal con- 

 tains a capillary of the same calibre as itself, and no cellular or other 

 pulp-tissue, for which, in fact, there is no room ; the canals were formed 

 by the enclosure of capillaries of the pulp in a calcified matrix. True 

 dentinal tubes may coexist with the large capillary canals ; but if they 

 do, they radiate from the central pulp-chamber and not from the canals : 

 in the most typical vaso-dentine, such as that of the hake, the matrix is 

 solid and there are no true dentinal tubes. Yaso-dentine is developed 

 from a sharply defined " membrana eboris," or layer of odontoblast cells. 



Osteo-dejsttijste, on the other hand, is also permeated by a system of 

 large channels, but these do not (except as an accident) contain capillary 

 blood-vessels, nor were they developed around capillaries. True " den- 

 tinal tubes " can perhaps hardly be said to exist ; but the tubes of small 

 calibre which do exist radiate, not from a common pulp-chamber, but 

 from the several canals. 



Its greatest distinction from vaso-dentine lies in the manner of its 

 development. It is not (if we except a thin outer layer of hard dentine 

 with which it is often clothed) developed from a specialized layer of odonto- 

 blast cells ; but calcifying trabecule shoot rapidly from the interior of 

 the first-formed dentine cap through the wmole substance of the formative 

 pulp, and the canal-system ultimately formed is due to the partial coa- 

 lescence of these ossifying trabecular leaving interspaces between them. 

 The canals have therefore nothing whatever to do with the blood-vessels 

 of the pulp, and therefore do not correspond very closely with those of 

 vaso-dentine. Osteo-dentine is thus not derived from the calcification 

 of a " membrana eboris," or special layer of odontoblast cells, but by ossi- 

 fication (of cells like osteoblasts) shooting through its whole mass. 



Thus the tooth-pulp can be bodily withdrawn from a tooth consisting 

 of vaso-dentine by tearing across the capillaries only, and the interior 

 of the dentine cap will be left smooth ; but the pulp can by no possibility 



