106 



TERTIAET VEETEBEATA OF THE PAYtM. 



Upper Dentition. — There are three pairs of incisors. The first pair (PI. X. fig. 3, i. 1) 

 are in close contact in the middle line ; they are comparatively small, downwardly 

 directed, prismatic teeth, each implanted in the premaxilla by a long backwardly 

 curved root. Their transverse diameter is roughly '8 cm. The second incisors {i. 2) 

 form great downwardly directed tusks. Their anterior face is strongly convex, the 

 posterior slightly flattened ; the tooth as a whole is strongly curved and tapers 

 somewhat towards the root, which, in the adult at least, is closed. There is an oblique 



Text-fig. 41. 



V. ^irif 



Cast of the cranial cavity of Mceriihenum lyonsi : A, from above ; B, from right side. 



ch., cerebellum ; f.l., frontal lobe ; inf., pituitary body ; p., pseudosylvian depression ; o.l., olfactory lobe ; 

 t.l., temporal lobe ; V., base of fifth nerve. | nat. size. 



wear-surface on the posterior side of the crown. No suflaciently weU-preserved 

 specimen has been found to show whether the enamel-covering was complete or not. 

 In one skull these tusks project some 4'8 cm. from the jaw, but as their ends are 

 broken off above the commencement of the wear-surface, it is probable that when 

 complete they protruded at least half as far again ; in this specimen the antero- 



