342 Proceedings of Royal Society of Edinburgh. [sess. 
in the other examples given, namely, as if the tooth were rotated 
on its long axis slightly backwards and inwards at its free extremity. 
Besides exhibiting this spiral rotation, these teeth are generally 
also very much bent or arched, the arch in some cases measuring 
fully half a circle. Neither this arching, however, nor certain 
curvatures necessarily resulting from following the contour of the 
jaw in which they are for so long a distance deeply implanted, 
interfere with the axial spiral under notice being easily traced. 
The foregoing examples are selected from among teeth of persis- 
tent growth, or where the pulp-structures continue the development 
of the tooth during the animal’s lifetime. In such teeth, however, 
as those where growth and development cease with the completion 
of the fang or root, the same principles are exhibited in their con- 
formation. Many of these teeth are bent or arched like some of 
those previously mentioned. In those which best display this 
formation, the crown and fang appear like two cones united by their 
bases, such as the canines of the Carnivora (fig. 4). Viewed in profile, 
they commonly present a crescentic form, extending from the free 
extremity of the crown to the termination of the root ; the arc thus 
formed, however, being in all of them comparatively inconsiderable. 
With regard to the spiral in their long axis it is different ; this 
character is quite apparent in all, and in many of them is equally 
well-marked, as it is in those already specified, and the line of 
torsion is in the same direction — namely, from the mesial side of 
the fang diagonally across the front of the tooth to the distal 
side of the crown. Among teeth of this character some fair 
examples are presented by the Seals. The simplest type of tooth 
in these animals is that where it consists of two cones united by 
their bases — the smaller cone forming the crown, the larger and 
somewhat ovate-shaped one forming the fang. The whole tooth is 
bent till it approaches an arc of about a quarter of a circle ; and if 
such a tooth be imagined to be grasped at the crown by the finger 
and thumb of one hand, and at the fang end by the finger and 
thumb of the other, and the two extremities be supposed to be then 
rotated for a quarter of a turn in ojDposite directions, it will enable 
the configuration of the tooth to be realised. Much the same may 
be said of such teeth as the canine in the Lion, Tiger, Bear, Ac., 
where very similar characters are presented, both in the bend and 
