220 
Mr. Corse’s Observations on the 
internal addition of new matter, till the cavity is entirely filled 
up. (Tab. XII.) 
This lengthening of the roots is necessary, to give that por- 
tion of the grinder in use sufficient firmness in the jaw, as well 
as to keep the surface at a proper level above the gum. That 
the alveolus shoots up between the roots, instead of the roots 
striking deeper into the sockets, as they lengthen, is obvious 
from Tab. VI. VII. and XI. ; where, a line drawn along the 
points of the roots, will follow the direction of those parts of 
the grinder which have not any roots. 
When the anterior teeth are worn down to the roots, these, 
with the sockets, begin to be absorbed, to make room for their 
successors, which are coming forwards. 
The shape of a grinder of the lower jaw is very different 
from that of one of the upper : in the latter, the grinder ad- 
vances from behind straight forwards, and the back part has a 
very convex shape ; whereas, the lower grinder advances rather 
in a. bent or curved direction, adapting itself to the shape of the 
jaw. (Tab. XI.) 
The surface of this grinder is somewhat of a concave figure, 
adapted to the form of the corresponding grinder in the upper 
jaw. The upper and lower grinders, (Tab. VIII.) and the sec- 
tion of a grinder, (Tab. XII.) shew, in the clearest manner, the 
progress of ossification in the roots, and the manner in which 
the different teeth are joined. 
In a young elephant, soon after birth, the milk grinders, 
with their roots, are completely formed ; and, even the succeed- 
ing or second set of grinders have the roots partly added to 
some of the anterior teeth, which are soon to cut the gum ; but 
the posterior layers are then without roots. (Tab. VI. Fig. 1.) 
