28 
MB. C. S. TOMES ON THE STRUCTURE AND 
The teeth of the common Hake throw so much light upon the question to 
be discussed that I will commence by a description of their minute structure. 
They are conical, slightly recurved, and very sharply pointed, being furnished 
with a sort of spear-point of enamel (see a, fig. 1, Plate 3), as are the teeth of all the 
Gad id 90 which I have been able to procure.* They are arranged in a double f 
row round the margins of the mouth, the outer row being firmly anchylosed, 
and the inner row set upon an elastic hinge, which allows them to bend inwards 
towards the mouth, like the hinged teeth of the Lophius piscatorius (see page 41 of 
this paper) ; the teeth situate near to the front of the mouth of a Hake which 
weighed 11 lbs. (in poor condition) are ^ of an inch in length. The teeth are hence 
rather conspicuous, and they are made more so in a freshly -caught fish by their 
bright red colour ; the dentine is very transparent, and the pulp is richly vascular, 
so that the red blood is seen through the exterior of the tooth, in the tubes of the 
dentine of which it, as will be presently seen, actually circulates. 
When viewed with a low magnifying power the axial pulp-chamber is usually 
seen to be of large size relatively to the whole tooth, and the dentine to be permeated 
through the greater part of its thickness by a system of canals which spring from the 
pulp cavity (see fig. 1). 
These canals are of almost uniform diameter in the different parts of their course, 
measuring from yooo f° 25*00 °f an inch in diameter ; they are arranged with great 
regularity, radiating outwards from the pulp cavity, and terminating by anastomosing 
with neighbouring tubes, forming squarish- ended loops towards the surface of the 
dentine. Owing to this flattening of the ends of the loops and to the tubes all 
stopping short at the same distance from the surface, an outer layer of dentine into 
which no such tubes penetrate is sharply marked off ( d in fig. 1). 
No fine dentinal tubes are given off from these canals, which do, however, here 
and there give off quite short prolongations of smaller calibre ; these are not, either 
from their size or frequency of occurrence, of much importance. 
But the point of greatest interest about the teeth of the Hake is the nature of the 
contents of these larger tubes. Each tube contains a capillary blood-vessel, and nothing 
else ; the thin wall of the capillary being in actual contact with the hard dentine of 
the completed tooth, and no other soft tissue being interposed. In fact, the tubes 
in the dentine are just the size of the capillaries of the pulp, and red blood is circulating 
through the capillaries enclosed in the dentine when the tooth is in use, just as it 
might be circulating in the capillaries of the pulp prior to its calcification. Thus 
blood is brought close to the surface of the dentine, and this, with the abundance of 
the tubes, it is that gives to the tooth of the living or freshly-killed Hake its 
brilliantly red colour. 
* Namely, the Cod ( Gadus morrhua), Haddock (G. ceglefinus), Whiting (Merlangus vulgaris), Coalfish 
(M. carbonarius), Pollack (M. pollachius), Hake ( Merlucius vulgaris), and Ling ( Lota molva). 
f They are often, owing to a fact respecting their attachment to he presently described, supposed to 
form a single row only. 
