the Teeth of graminivorous Quadrupeds . 239 
Teeth formed in this way, are composed of two parts, of dis- 
similar texture : one, the enamel, which is striated ; the others 
the substance of the tooth, which is laminated, like ivory, be- 
ing more compact than common bone, and less so than the 
enamel ; but differing from both in the mode of its formation. . 
Bones are formed in two different ways : those that are cy-t 
lindrical, have cartilage for their basis; those that are flat, either 
cartilage or membrane; but, in no instance in the body are 
they formed upon a pulp. The substance of the tooth must 
therefore be considered as distinct from bone, and may be rank- 
ed, both from its structure and mode of formation, as a species 
of ivory.* 
The teeth of the elephant differ from those just described, in 
being composed of a great many flattened oval processes; these, 
while growing, are detached; but, when completely formed, their 
bases unite together, and make the body of the tooth, to which 
the fangs are afterwards added; and, as the fangs are length- 
ened, the tooth rises in the jaw. This is what may be considered 
as the tooth itself, being composed of the same materials as the 
teeth of carnivorous animals ; but, in addition, there is another 
substance, which unites all the processes together, laterally, into 
one mass ; this is softer than the substance of the tooth, and, 
upon examination, proves to be similar, in its texture and forma- 
tion, to common bone. 
• The tasks of the elephant are formed upon a pulp, similar to teeth. 
Tumors are sometimes met with in the frontal sinuses of the human body, having 
a perfect resemblance to ivory; they have their origin in the bony cavity of the-sirius, 
and extend themselves into the orbit of the eye. Of these, I have seen two instances, 
and was ufiable, at the time, to account for them ; but am now induced to believe they 
were formed upon vascular excrescences, growing from the lining of the sinuses, similar 
in their organization to the pulps above mentioned. - 
I i 2 
