1894 - 95 .] Dr J. Smith on the Mammalian Tooth. 339 
length occurring in numerous well-known examples among these 
organs. This bend or arching, extending from the alveolar attach- 
ment to the crown extremity of the tooth, forms, in many animals, 
an arc equal to the greater part of a circle, or is even somewhat 
more extensive, a complete ring being occasionally constituted by 
the tooth, the tip or free extremity returning to a spot somewhere 
about the situation of the formative pulp. The general rule, how- 
ever, is, that the arc thus formed is not that of a circle described 
upon one plane, or of a discoid character, but oblique in the course 
it follows, so that the free extremity, instead of impinging upon, 
passes on one or other side of the alveolar or maxillary end of the 
tooth, the primary curve again being at the same time of such a 
nature that, instead of a ring, it approaches in character more to a 
logarithmic spiral. 
The upper canine or tusk of the Walrus affords an example where 
some of these morphological features are easily discernible (fig. 7). 
This tooth projects downwards at about a right angle with the jaw, 
and is so bent as to form an arc of a very large circle, having the 
convexity directed forwards and somewhat outwards. The body of 
the tooth consists of a very elongated and laterally compressed cone, 
so that a transverse section of it would exhibit an oval or elliptical 
form. The bend in these organs is too apparent to require any 
remark ; but that a spiral turn is also given to them on the long 
axis, may, in addition to what is perceptible on mere ocular inspec- 
tion, be demonstrated by looking at the two cut surfaces of any 
cross section, when the varying direction in the vertex diameter of 
the ellipse presented at either end will indicate the twist or turn 
on its long axis which the tooth is taking. 
So far, again, as concerns the bend taken by the Walrus tusk, 
a much more pronounced arc is described by those of some other 
animals ; a circumstance occasionally interfering with the axial 
torsion being so clearly followed out. The incisors of the Elephant, 
the canines of the Hippopotamus, the enormous tusks of the extinct 
Mammoth, &c., describe, in the arc presented by some of them, a 
large portion or even the whole of a circle, so deflected outwards, 
however, that instead of a true ring it forms one of 'those curves of 
double curvature already spoken of, thus enabling the free extremity 
to pass on one side of the animal’s head. The long axis twist. 
