MORI'IIOLOOY OF THE J3RAIX IX THE MAMMALIA. il'l 



llio Leiinirs as a wliolo. It' avo examine tlie few reconls which arc quoted al)ove, and 

 compare them Avith data ohtaiued from othin- mammals in exactly the same manner hy 

 the same investigator, it w ill then be seen from a comparison of the hody-weii^hts of 

 those non-Primate mammals which possess the same absolute brain-weights as various 

 Lemurs, that the proportion of brain to body is considerably hi^-her in th(« latter. 



Compare the series of brain-weights in the genus Lemur, wiiieli vary from 21-1 grm. 

 to 39-1 grra. (representing the followinij proportions of brain to body : — 1 : GO, 1 : To, 

 1 : 7<'), 1 : 8f, and the exceptional 1 : 103), with the following measurements (jf 

 Carnivora : — 



liniin- Pi-djiDrl'ioii to 



Spi:(1i:s. irfir/lit. Iliiihj-u-niiht. 



I'ircrru taii(/(il(iiii;a, VtViiy '.\() 2 1 : lo;} 



Fclis cutKs, Liiui '.VJA\ ] : lO;, 



1-yh domcslica, Uui :W-5 1 : [() [ '^"' '"-'"^-^^ "*' 



l 7 niPU'suroiiKMits. 



, ;52 1 : ]2S 



('fiiii.<! /ar/oj/>is, Ijinn. .'51 \ :•>()'>) 



„ .'iD-l 1 : S4. i 



Pdiiuloi iiriis miixdiij/ii, (ir:iv 'I'l 1:111 



Ciilict's vittdld, Sclnx-h 21-1 1 : !»I 



HiTjiestfs all/'icdiiilii, Ciiv 2'.Vi 1 : 81 



In all of these Carnivora the proportion of the brain-weight to th(^ body-weight is less 

 (and in many cases very considerably so) than it is in Lemurs with brains of a corr(>- 

 sponding size. And in other mammalian Orders the disproportion in the size of the body 

 per unit of brain-weight is even more pronounced. The Lemurs ;ill have relatively 

 large brains in comparison with other mammals, but are much uku-c; poorly endowed in 

 this res])ect than the Apes. 



The data are too scanty to enable us to decide whether this difference in the brain- 

 weights of .Vpes and Lemurs is due merely to the failure of the latter to keep ])ace in 

 brain-growth with the former, or is the result of an actual reduction in size. 



The most noteworthy distinction between the brain of the Lemurs aiul the A])es is the 

 relative size of the olfactory regions of tli<' brain. 



The l)rain of the Ajjcs is distinctly uiicrosmatic. The olfactory bulb is very sniall, 

 and is borne on a long attenuated peduncle ; the anterior part of the i^yriforni lobe is 

 so reduced as to be recognizable with difliculty, and the posterior part is so small that it 

 is almost always confined to the ventro-mesial aspect, and rarely extends on to the 

 lateral as^iect of the hemisphere ; ami the liippocam])us is relatively very small. 



In mammals the size of the olfactory parts i>f the brain is subject to great 

 A'ariations. 



Thus in all aquatic mammals they b(!come greatly reduced in size [e. cj. in Orniiho- 

 rhijuchus, the Pinnipedia, the Sirenia, the Cetacea), or even entirely absorbed (in the 

 Odoutoceti). In mammals which lead an arboreal life they ai"e relatively smaliei' than 

 in those which lead a terrestrial existence, e. ij. the rhineacephalon is relatively much 



