MCEEITHEEIUM. 



107 



posterior diameter of the base of the tusk is about 2-8 cm., the lateral diameter the 

 same. The third incisor (i. 3) was a small tooth, nearly circular in section, and 

 situated immediately behind the tusk, just internal to its outer angle. This tooth is 

 represented by its alveolus only in all specimens examined ; the antero-posterior 



Text-fig. 42. 



Cast of the cranial cavity of Mastodon americanus : A, from above ; B, from right side. 

 rb., cerebellum ; f.l., frontal lobe ; p., pseudosylvian depression ; o.l., olfactory lobe ; t.l., temporal lobe. 



^ nat. size. 



p 2 



