Xlii INTRODUCTION. 



In the cells of the dentinal pulp the nucleus fills the parent 

 cell with a progeny of nucleoli before the work of calcification 

 begins : in the enamel-pulp the nucleus of the cell disappears, like 

 the cytoblast of the embryo plant in the formation of most vegetable 

 tissues : in the cells of the capsule, the nucleus neither perishes nor 

 propagates, but retains its individuality, and gives origin to the 

 most characteristic feature of the cement, viz : — the radiated cell. 



The primordial material of each constituent of the tooth-matrix 

 is derived from the blood, and special arrangements of the blood- 

 vessels pre-exist to the development and growth of the constituent 

 substances. A pencil of capillaries is directed to a particular spot 

 in the primitive dentiparous groove, and terminates there by a looped 

 net-work, from which spot a group of nucleated cells begins to 

 arise in the form of a papilla. The cells of the papilla are, however, 

 colourless, and the plexus of capillaries is confined to its base. 

 In the Mammalia (embryo Calf of three inches in length) membra- 

 nous septa are formed, into which the vessels extend, which cross 

 the groove and inclose the papilla in a follicle. From the free 

 margin of this follicle the processes are developed, which indicate 

 the configuration of the future crown of the tooth, and, in the 

 molars of the calf, subsequently develope the re-entering folds on 

 which the complex structure of the crown of the molar tooth 

 depends. 



The primary dentinal papilla and its capsule rapidly increase 

 by successive additions of nucleated cells, apparently derived from 

 material supplied by the capillary plexus at the base ; the capillaries 

 now begin to penetrate the substance of the pulp itself, where they 

 present a sub-parallel or slightly diverging penicillate arrangement, 

 but preserve their looped and reticulate termination near the apex 



