44 
MR, C. S. TOMES ON THE STRUCTURE AND 
the inner side of the tooth extends to a lower level than the outer side, and is firmly 
bound down by dense ligamentous fibres (2 in fig. 25) to the bone beneath it. 
On the opposite side, however, it is of different form ; the dentine terminates in a 
sort of shoulder (2' in fig. 25), which abuts upon a surface of bone shaped so as to fit 
it ; to this it is bound down by a band of ligamentous fibres, but in such a manner as 
to allow of a certain small degree of motion, the extent of which will readily be 
appreciated by an inspection of fig. 25. 
Thus in the Cod the outer side of the tooth, which was altogether free in the 
Hake, is so attached as to allow of slight mobility only. In other members of the 
family, e.g. the Haddock and the Coalfish ( Gadus carbonarius), the base of the tooth 
is furnished with a similar sort of shoulder round its whole circumference, and by this 
it is fitted upon and into a short supporting cylinder of bone (see fig. 24). 
This arrangement of course allows of practically no mobility whatever, and the 
Haddock, the Cod, and the Hake thus present three very instructive steps in the 
production of a highly specialised organ. The degree to which the little shoulder 
of dentine is fitted within the osseous cylinder beneath it varies much in different 
genera and species, but an attachment of this kind, completed by a few slight 
ligamentous fibres binding the parts together, may be taken to be the rule in Gadidse 
and Pleuronectidae.* 
Description of Figures. 
a. Enamel. 
b. Vascular dentine. 
c. Bone of jaw. 
c. “ Bone of attachment.” 
c". Specialised buttress of bone of attachment. 
d. Hard dentine. 
d'. Modified vascular dentine. 
e. Formative cells of enamel-organ. 
f Finely tubular dentine in osteo-dentine tooth. 
g. Large canals of osteo-dentine. 
h. Calcifying trabeculae — osteo-dentine. 
i. Osteoblast cells. 
k. Cellular tissue external to developing tooth (fig. 23 only). 
* Since the foregoing paper has been in the hands of the Royal Society, I have found, that the teeth in 
Certain parts of the month of the common Pike are hinged ; a description of the mechanism by which 
they are attached, which is very remarkable, will be found in the ‘ Quarterly Journal of Microscopical 
Science,’ January, 1878. 
