MOKKITIIKKIUM. 15 



.posterior portion, is entirely altered by it (see the broken 

 skull of the Indian elephant in Gallery). The reason for 

 this swelling of the bones is that, as the head becomes 

 heavier, owing in great part to the development of the trunk 

 and tusks, a' larger surface for the attachment of the muscles 

 which support the head is necessary, and even in the small 

 Eocene Moeritherium change in this direction had begun. 



In Moeritherium the dental formula (see p. 9) is I. ^, C, J, 

 Pm. |, M. |= or thirty-six in all (figs. 5 & 7). From the 

 formula it will be seen that in the upper jaw only one premolar 

 is wanting to complete the primitive number, while in the 



Fig. 6. 



Skull and lower jaw of Moeritherium from the Upper Eocene of the Fay urn, 



Egypt. 4 nat. size. 



ant.orb., antorbital foramen ; c., canine ; e.r.oc., exoccipital ; />'., 

 frontal; i. 1-3, incisors; ju., jugal; m. 1-3, molars; mx., maxilla; 

 n., nasal; p.a., parietal; par., paroccipital ; pm. 2-4, premolars; 

 p.mx., premaxilla; pt., post-tympanic process of squamosal ; s.oc., supra- 

 occipital ; sq., squamosal. 



lower jaw an incisor and the canine are missing on each side 

 in addition to one premolar. 



Of the upper incisors the second pair (i. 2) are greatly 

 enlarged and form strong downwardly directed tusks, the 

 beginning of the great tusks so characteristic of the later 

 elephants. The canine (c.) seems to have been quite small and 

 unimportant, being on the way to disappearance. The pre- 

 molars (pm.) are separated from the canine by a short interval, 

 and, as already mentioned, the anterior one of the full denti- 

 tion is wanting. The remaining premolars are all simpler in 



