the Teeth of graminivorous Quadrupeds. 
257 
Tab. XIX. 
Fig. 1. A side view of the skull of the young Sus 2 TLthiopicus s 
to show the mode in which the grinders come forward, as the 
large one increases in size. 
Fig. 2. A side view of the full grown grinder tooth. 
Fig. 3. A transverse section, polished, to show the mixture 
of bone with the enamel and substance of the tooth, and the 
particular appearance of the processes. 
Tab. XX. 
Fig. 1. A transverse section of the horse's grinding tooth, po- 
lished, to show the relative situation of the bony part, with 
respect to the enamel and substance of the tooth. Two por- 
tions of it are inclosed by enamel, and a third portion is on the 
outside of the tooth altogether. 
The two holes were probably to give passage to arteries, and 
were enlarged by the food falling into them, and wearing away 
their sides. 
Fig. 2. A similar section of a grinding tooth of the cow. The 
shape of the bony portions inclosed by the enamel is different, 
and there is a smaller portion of bone on the outside of the 
tooth. 
Fig. 3. A similar section of a grinding tooth of the sheep. 
The portions of bone inclosed by the enamel are very small, and 
there is none on the outer side of the tooth. 
Fig. 4, 5, and 6 . Are three sections of a grinding tooth of the 
hippopotamus, to show that there are portions of enamel inter- 
mixed with the substance of the tooth, but no bone whatever. 
