450 



CERVUS. 



side of the tooth. The concavities and convexities are 

 reversed in the grinders of the lower jaw. The sum- 

 mit of each lohule, 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 (e, e) 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 inner lobules (id) 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 Bomda. 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 



