in North America of rare Extinct Vertebrates. 221 



In the fossil skull of a herbivore from an older division of the 

 Eocene ("I'^oc^ne ^ Lophiodons" d'Issel), Ed. Lartet* found 

 the brain, as represented by the cast in matrix, to be still less, 

 relatively, than in the Anoplothere and Cainothere. The 

 hemispheres extended neither upon the rhinencephalon in front 

 nor upon the cerebellum behind. He also notes the lower 

 development of the brain in the Miocene Hipparion as com- 

 pared with that of a modern Equus of similar bulk. Referring 

 to the size of the much-convoluted cerebral hemispheres of 

 the brain in the elephant, and assuming the natural duration 

 of life of that animal to be 150 years, associating also the 

 longevity of Man with his large brain f, Lartet infers that the 

 older the mammal in geological time the briefer was the life 

 of the individual and the smaller the amount of its intel- 

 lectual faculties \. 



When, however, we consider the small size of brain and the 

 great length of life of a gigantic tortoise, the correlation sup- 

 porting the induction of the briefer life-periods of the indivi- 

 dual herbivores of the Miocene and Eocene periods is far from 

 commending itself to credence. As to the limitation of intel- 

 ligence associated by Gratiolet and Lartet, as by Cuvier, with 

 the low development of brain, that is the obvious physiologi- 

 cal inference. 



The question, which is here left untouched, is. What were 

 the conditions of existence in the older tertiary times which 

 rendered better brains and concomitant intelligence uncalled 

 for in the peaceful Herbivora of those periods ? 



To the attempt to solve this question I was led by observing 

 that an Eocene marine mammal showed the same inferiority 

 of development of its cerebral liemispheres, compared with its 

 modern congeners, as did the terrestrial forms §. And the 



* Comptes Rendus de I'Acad. des Sciences, Juin 18G8. 



t " L'elepbant, qui vit im siecle et demi, a le cerveau plus o-rand 

 qu'aucun autre manimifere terrestre ; apres I'elepliant viendrait I'homme 

 qui, par le volume absolu du cerveau, commepar lalongevite, parait I'em- 

 porter sur les autres mammiferes terrestres." — Loc. cit. 



X " II en ressortirait comme hypotbese explicative des faits observes, que, 

 dans certains divisions de la classe des mammiferes, il y aurait eu, depuis 

 leur apparition sur le globe, accroissement graduel d'energie vitale et 

 d'intelligence ; en termes plus explicites, que la duree de vie et le develop- 

 pemeut des facult^s intellectuelles auraient ete moiiidres chez les especes 

 fossiles remontant aux premiers temps de la periode tertiaire que leurs 

 analogues ou leurs congeneres de I'epoque actuelle." — Loc. cit. 



§ " Viewing fig. 2 (brain of Eotherium) in contrast with fig. 5 (brain 

 of Manatns), one is led to speculate on the circumstances influencing in- 

 crease of brain-mass in marine mammals of simple, sluggish, Sirenian 

 habits, either obtaining their food from seaweed at no great depth, or 

 shuffling along to browse the grassy shore of a river or estuary. Certain 

 it is that since the good old Eocene times ' new foes have arisen ;' and any 



