Cuap. VII. Structure of the Brain. 20 1 



Rolleston, Mr. Marshall, M. Brora and Professor Turner. At the 

 conclusion of a special paper on this subject the latter writes : 72 



3 The three specimens of the brain of a chimpanzee just described, 

 " prove, that the generalisation which Gratiolet has attempted to draw of 

 " the complete absence of the first connecting convolution and the 

 '* concealment of the second, as essentially characteristic features in the 

 u brain of this animal, is by no means universally applicable. In only one 

 ** specimen did the brain, in these particulars, follow the law which 

 " Gratiolet has expressed. As regards the presence of the superior bridg- 

 *• ing convolution, I am inclined to think that it has existed in one hemi- 

 ** sphere, at least, in a majority of the brains of this animal which have, up 

 " to this time, been figured or described. The superficial position of the 

 u second bridging convolution is evidently less frequent, and has as yet, 

 " I believe, only been seen in the brain (A) recorded in this communi- 

 u cation. The asymmetrical arrangement in the convolutions of the 

 '* two hemispheres, which previous observers have referred to in their 

 " descriptions is also well illustrated in these specimens." (pp. 8, 9.) 



Even were the presence of the temporo-occipital, or external per- 

 pendicular, sulcus a mark of distinction between the higher apes and 

 man, the value of such a distinctive character would be rendered very 

 doubtful by the structure of the brain in the Platyrhine apes. In fact 

 while the temporo-occipital is one of the most constant of sulci in 

 the Catarhine, or Old World, apes, it is never very strongly developed 

 in the New World apes ; it is absent in the smaller Platyrhini ; 

 rudimentary in Pithecia ; 73 and more or less obliterated by bridging 

 convolutions in Ateles. 



A character which is thus variable within the limits of a single group 

 can have no great taxonomic value. 



It is further established, that the degree of asymmetry of the convolu- 

 tion of the two sides in the human brain is subject to much individual 

 variation ; and that, in those individuals of the Bushman race who have 

 been examined, the gyri and sulci of the two hemispheres are consider- 

 ably less complicated and more symmetrical than in the European 

 brain, while, in some individuals of the chimpanzee, their complexity 

 and asymmetry become notable. This is particularly the case in the 

 brain of a young male chimpanzee figured by M. Broca. (' L'ordre 

 des Primates," p. 165, fig. 11.) 



Again, as respects the question of absolute size, it is established that 

 the difference between the largest and the smallest healthy human 

 brain is greater than the difference between the smallest healthy 

 human brain and the largest chimpanzee's or orang's brain. 



Moreover, there is one circumstance in which the orang's and chim- 

 panzee's brains resemble man's, but in which they differ from the lower 

 apes, and that is the presence of two corpora candicantia — the 

 Lynomorpha having but one. 



in view of these facts I do not hesitate in this year 1874, to repeat 

 and insist upon the proposition which I enunciated in 18G3. 74 



"So far as cerebral structure goes, therefore, it is clear that man 



72 Notes more especially on the 73 Flower 'On the Anatomy of 



bridging convolutions in the Brain I Ithecia Monachus' 'Proceedings o\ 



cf the Chimpanzee, 'Proceedings of the Zoological Society,' 1862. 



the' Royal Society of Edinburgh,' 74 'Man's Place in Nature,' p. 102 

 1865-6. 



10 



