422 ON THE GROWTH AND STRUCTURE 
Explcmation of Plate X. 
Fig. 1. Shews the tooth of the Rattle-Snake at an early 
stage of its formation. The line marked on the 
dorsal or convex side of the tooth, is already com- 
pletely ossified. 
Fig. 2. The tooth farther advanced in its growth. The 
line, or supposed fissure, is firmly ossified at that 
isj near the anterior aperture of the poison-canal; 
but even at 6, where the parietes of the tooth are 
quite cartilaginous and soft, the line is not open, but 
perfectly closed. c marks the soft parts at the base 
of the tooth. 
Fig. 3. A portion of the external parietes of the tooth 
has been removed, by which the cavity (a) contain- 
ing its pulp is exposed, h marks the vertical or 
ascending lamina, uniting the poison-canal on its 
convex side to the inner surface of the parietes of the 
tooth. At no period is the poison-canal open, but at 
its extremities. 
Fig. 4. The tooth of the Kattle-Snake in a still more 
advanced state of growth. The aperture at the base, 
for the admission of the poison, is just formed; but 
the line on the convex surface is closed throughout, 
even at 6, immediately anterior to the aperture. 
Fig. 5. The tooth fully formed, but not yet fixed. A 
portion of the external parietes and pulp has been 
removed, exposing the poison-canal, tt. The nourish- 
ing and formative pulp of the tooth is found chiefly 
on the concave side, at 6. c marks the aperture at 
the base. 
