36 
MR. C. S. TOMES Oft THE STRUCTURE AND 
part and not the whole contents of the tube. In the fresh condition the channels of 
the dentine contain a firm cellular tissue, not unlike that which forms the bulk of 
most tooth pulps, but it is exceptional for it to be rich in vessels. 
The nature of the contents of the channels will be best understood by following out 
their development. 
Of the development of the Pike’s tooth Professor Owen (‘ Odontography,’ p. 133) 
tells us “ that the formation of a tooth is an act of conversion of the substance, 
and not of cells upon a formative surface of the pulp, is clearly illustrated in the 
Pike. The cone-shaped cap which the half-developed tooth forms upon the remaining 
matrix can only be removed by overcoming a certain resistance, and this resistance 
is seen to be due to the processes of the pulp which extend into the medullary 
canals of the tooth ; the broken ends of these processes give an irregular surface 
to the exposed pulp, and their continuation into the tooth may be seen by sawing the 
latter across. This connection between the substance of the tooth and of the pulp is 
still better seen in a finely injected specimen ; the mechanical relation between the tooth 
and the pulp is then seen to be of precisely the same kind as those between an ordinary 
osseous nucleus and the cartilaginous matrix in which it is developed ; it is in the course 
or direction of development that the chief difference exists ; in the tooth it is centri- 
petal, in the bony epiphysis centrifugal, but the mode of development is the same.” 
An early dentinal pulp from the jaws of a Pike does not present any special 
peculiarity ; it is a conical mass of richly cellular tissue, the surface of which is 
covered as by an epithelium, with a layer of larger elongated cells, which do not 
form so distinct and sharply defined a layer as the odontoblasts of most dentinal 
pulps. By the calcification of these the exterior layer of fine tubed dentine is 
formed in the ordinary way, and presents no peculiarities worth description. But 
no sooner is the thickness of this outer layer (f in figs. 13 and 14) completed, than 
the nature of the process of calcification becomes profoundly changed ; the remainder 
of the dentine is not formed by the calcification of the more or less defined layer 
of cells corresponding to the “ membrana eboris,” but by an extension of calcification 
through the mass of the pulp in a manner to be presently described. The surface 
of the pulp in immediate contact with the dentine already formed is no longer clothed 
with a continuous layer of odontoblasts, but the cells which are near to the surface 
become aggregated into masses, between which there appears an almost structureless 
transparent tissue, which then forms trabeculae shooting from the dentine into the 
substance of the pulp between the cellular aggregations. Calcification follows very 
close on the heels of the formation of this tissue, and a longitudinal section of a 
pulp at this stage (see fig. 15) shows the extent to which the whole mass of the 
pulp becomes penetrated by these calcifying processes. Their course as they run 
down into the pulp is not at all determined by the position of the capillaries, in 
which the pulp is not rich ; on the contrary, they extend in almost straight lines 
from the dentine already formed down into the pulp, and subsequently become 
