266 THE DESCENT OF MAN 



nal perpendicular sulcus by "bridging convolutions," on one 

 side or the other, has been noted over and over again by 

 Prof, fiolleston, Mr. Marshall, M. Broca, and Prof. Turner. 

 At the conclusion of a special paper on this subject the 

 latter writes:" 



"The three specimens of the brain of a chimpanzee just 

 described, prove that the generalization which Gratiolet has 

 attempted to draw of the complete absence of the first con- 

 necting convolution and the concealment of the second, as 

 essentially characteristic features in the brain of this animal, 

 is by no means universally applicable. In only one speci- 

 men did the brain, in these particulars, follow the law wnich 

 Gratiolet has expressed. As regards the presence of the 

 superior bridging convolution, I am inclined to think that 

 it nas existed in one hemisphere, 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 second 

 bridging convolution is evidently less frequent, and has as 

 yet, I believe, only been seen in the brain (A) recorded in 

 this communication. The asymmetrical arrangement in the 

 convolutions of the two hemispheres, which previous ob- 

 servers 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 ex- 

 ternal perpendicular, 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 tem- 



eoro-occipital is one of the most constant of sulci in the 

 atarrhine or Old World apes, it is never very strongly de- 

 veloped in the New World apes ; it is absent m the smaller 

 Platyrhini; rudimentary in Pithecia ;"" 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 convolution of the two sides in the human brain is 

 Nsubject 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 considerably 



'^ Notes more especially on the bridging convolutions in the Brain of tho 

 Chimpanzee, "Proceedinga of the Royal Society of Edinburgh," 1865-66. 



'2 Flower "On the Anatomy of Pithecia Monachus," "Proceedings of the 

 Zoological Society," 1862. 



