32 
MR. C. S. TOMES ON THE STRUCTURE AND 
cavity into the substance of the dentine ; these are about g-g^th of an inch in diameter 
at then origin, but they quickly divide, and their branches form anastomoses with 
those of the neighbouring tubes ; the loops thus formed by the smaller terminal 
branches constitute a well-defined boundary between the coarse central and the fine 
external dentine. 
“ In this latter the calcigerous tubes, which are about - f 5 ~ o oot h of an inch in 
diameter, proceed as usual, parallel to each other and parallel to the axis of the 
tooth at its apex, but transversely to that axis at its sides ” (‘ Odontography/ p. 163). 
The tooth of the Cod differs in some particulars from that of the Hake, so that 
it may be worth while for me to briefly describe its structure. 
Cod ( G . morrhua). — The teeth are not so slender as those of the Hake, and they 
are more solid, the pulp being smaller relatively to the size of the completed tooth. 
Just as has been described in the case of the Hake, the dentine of the Cod is 
permeated by a system of canals about in diameter, which form loops and 
anastomoses with one another, just as do the capillaries of the pulp prior to the 
commencement of calcification around them. These tubes contain, in the fresh 
condition, capillary vessels in which blood circulates ; in fact the only- difference 
between the dentine of the Cod and that of the Hake lies in the arrangement of 
the capillary channels, which are less abundant in the dentine of the Cod, and form 
loops with rounded instead of with flattened ends, so that the boundary of that 
external layer of dentine which is not permeated by the tubes is less sharply 
pronounced. In a longitudinal section there is faint striation running in the long 
axis of the tooth or rather parallel with its surface ; this is to be seen in all parts 
of the tooth, but the striation is most pronounced near to the base. 
Under a high power this appears (in longitudinal sections) like parallel tubes, about 
To (Tooth of an inch in diameter, but they do not start either from the pulp cavity or from 
the vascular canals, and there is an exactly similar appearance in the bone which 
supports the tooth (c in fig. 25). 
No coloured solution can be induced to enter them, even by boiling the thinnest 
sections in it, or by placing the sections immersed in the fluid under the receiver of an 
air-pump and exhausting the air as completely as possible. Nothing can be seen of 
tubes in transverse sections, and their direction is parallel to the long axis of the tooth, 
so that, if these striae are tubes, they are at right angles to the ordinary course of 
dentinal tubes, and at right angles to the long axes of the formative odontoblast cells. 
But the most conclusive evidence as to their not being the representatives of the 
dentinal tubes of other creatures is derived from an examination of the teeth of some 
members of another family, viz., the Pleuronectidse. In this family the teeth are com- 
posed of vaso-dentine of the same type as that possessed by the Gadidse, with this 
difference, that at their apices the dentine is poor in vascular canals, but is permeated 
by an abundance of true dentinal tubes. Passing downwards from the enamel-tipped 
apices of the teeth the vascular canals become more and more abundant, and the dentinal 
