INTRODUCTION. XXXVIl 



The dentine is transparent and consists of fibres which proceed from 

 the point to the base of the cone. The bone is traversed by canals, 

 which resemble the medullary canals of ordinary bone, except in 

 being less regular. The dentinal tubes are connected with these 

 medullary canals of the proper osseous substance, and it is plain 

 that the tubes are continued funnel- wise from the medullary canals. 

 The canals ramify in the dentine and as they proceed transversely 

 across the thickness of the tooth-cone, so they decussate the dentinal 

 fibres. Accordingly here the dentinal tubes correspond with the 

 medullary canals of bone not with the calcigerous tubes which radiate 

 from the bone-corpuscles. 



" A more certain knowledge of the whole structural relations of 

 dentine seems to be only possible when its development is studied in 

 very differently constructed teeth. "(1) 



The main facts, then, which may be considered as established by 

 the researches of Purkinje and Schwann, relative to the formation of 

 dentine and the changes which the dentinal pulp undergoes during 

 that process are the following : the proper tissue of the pulp consists 

 of minute nucleated cells, with capillary vessels and nerves, invested 

 by a dense structureless membrane (2) which disappears during 

 the formation of the dentine. The superficial pulp-cells as- 

 sume an elongated form ; they correspond in diameter and 

 direction with the tubes of the contiguous cap of dentine. These or 

 similar cells are observed, in a state of transition into dentine, in the 

 interspace between the pulp and the previously formed cap of den- 

 tine ; they adhere to the latter when it is displaced from the pulp. 



(1) Schwann, loc. cit. p. 128. 



(2) The capsule of the entire dental matrix will be understood to be quite a distinct part 

 from the * preformative membrane ' of the pulp. 



