THE SIGNIFICANCE OF THE INGREASED SIZE 



OF THE CEREBRUM IN RECENT 



AS GOMPARED WITH EXTINGT MAMMALIA 



by E. RAY LANKESTER MA. T. R. S. 



DIRECTOR OF THE NATURAL HISTORY DEPARTEMENT OK THE BRITISH MUSEUJI 



CORRESPONDENT OF THE INSTITUTE OF FRANCE 



H ON. MEMBER OF THE BIOLOGICAL SOCIETY OF PARIS 



It has occured to me that in order, at short notice to take part in ttie 

 célébration of the Biological Society of Paris — liowever briefly. — I might 

 place before my colleagues a biological problem and suggest a solution of 

 it which though not décisive has, 1 think, much in its favour and raises 

 many interesting points for observation and discussion. It is well established 

 that the extinct Mammalia of the middle of lower Tertiaries had — as com- 

 pared with their nearest living congeners — an extremely small cerebrum. 

 The exact figures are not important, but Titanotherium — a true Rhinocéros 

 — had certainly not more than one fifth of the cérébral nervous substance 

 which is possessed by living Rhinocéros. Dinoceras representing a distinct 

 group of Ungulata had even a smaller brain. Yet in bulk thèse animais 

 were as large as or larger than the largest living Rhinocéros. Further, it 

 appears from the examination of the cranial c avilies of extinct and récent 

 Reptiles, that the increase in the size of cerebrum is not peculiar to Mamma- 

 lia, but that we may assert as a gênerai proposition, that récent forms bave 

 a greatly increased bulk of cerebrum as compared with their early Ter- 

 tiary or^mesozoic fore-bears. 



It appears also that the relative size of the cerebrum in man and the 

 anthropoid âges may be cited hère as a similar phenomenon; the more 

 récent genusHomo having an immensely increased massof cérébral nerve- 

 tissue as compared with the more ancient pithecoid gênera. 



The significance of this striking fact — viz. that récent forms hâve a 

 cérébral mass greatly larger than that of extinct forms (probably in every 

 class of the animal kingdom) — has not been discussed or considered as it 



