450 CERVUS. 
side of the tooth. The concayities and conyexities are 
reversed in the grinders of the lower jaw. The sum- 
mit of each lobule, or division of the lobe, thus pre- 
sents a crescentic figure, and, when worn by mastica- 
tion, exposes a body of dentine (od, id,) with a raised 
border of enamel, coated thinly by cement. ‘The cres- 
centic fissures (¢, ¢) between the lobules, are filled partly 
by cement, partly, in the recent Ruminant, by masticated 
food ; and when the tooth is much worn, they are divided 
from each other, and separately inclosed by a crescentic 
island of enamel: the entire circumference of the com- 
plex molar being also invested by a coat of enamel and a 
thinner layer of cement. 
In the Megaceros the imner lebules (¢d) are thicker 
transversely than in the Aurochs, the crescentic enamel 
islands are narrower and more simple, and the cemental 
cavity of each is continued into the other until a later 
period of attrition. In the Elk, the central crescents inter- 
communicate for a still longer period, and the crown of the 
molar is cleft by a crucial incision. There is a small 
accessory column (d@) at the internal interspace of the lobes 
of the tooth in both Alces and Megaceros, which is not pre- 
sent in the Rein-deer ; but it is confined to the base of the 
fissure, not developed to such a length as in the molars of 
the Aurochs and other Bovide. With regard to the pre- 
molars, which may be compared to a single lobe of the 
true molars, the central crescentic island of enamel is 
more complex than in the Aurochs, the inner border 
forming a fold near its back part which extends to the 
outer border. In the lower jaw the first and second pre- 
molars are relatively larger and more complex than in the 
Aurochs. I have been led into these details on account 
of the close correspondence in size between the teeth of 
