MORPHOLOGY OF THE CEREBRAL CONVOLUTIONS. 287 



a less extent than in the brain of the negro, thus occupying in this respect an inter- 

 mediate position between the negro and white, a condition we might almost a priori 

 be led to expect. Plate XLI, fig. 1, and Plate XLII, fig. 1, are drawings from 

 photographs of two negro brains, and it will be seen that, owing to the develop- 

 ment of the ascending or perpendicular branch of the Sylvian fissure the third 

 frontal convolution is deficient just over the position of the Island. 



This peculiarity of the negro brain, although it is foetal in its character, has 

 not been found in the brains of any of the adult Primates with the exception of 

 some of the Anthropomorpha. Pansch has stated that he has found it not only in 

 the gorilla but also in a chimpanzee and in an orang brain. It must, however, be 

 exceptional in the two latter species. I have had the opportunity of studying the 

 brains of two chimpanzees and one orang and in none of these was it present, as 

 may be seen in the figure of the chimpanzee brain, Plate XXXIX, fig. 4, where, 

 although the ascending Sylvian, a. s., is present and well developed, the Island is 

 entirely hidden. Bischoff also states that he has observed it in the brain of a gorilla 

 and also in a female orang brain. Neither the descriptions nor the plates of anthro- 

 poid brains given by Owen, Yrolik, Tiedemann, Turner, Rolleston, Marshall, Gratio- 

 let, or Duvernoy give this condition as existing, nor is the Island stated specially to 

 be covered. Huxley, 1 however, gives a plate and also makes the statement that the 

 insula is uncovered. In all other Primates as far as known the anterior branch of 

 the Sylvian is either rudimentary or does not develop, and as a result the Island is 

 never exposed. It would appear, therefore, that this condition is found only in the 

 negro and higher apes. 



The Sylvian fissure begins at the base of the brain back of the point of origin 

 of the olfactory nerves. It runs thence outward and then ascends obliquely 

 upward and backward. In respect to the general direction of this fissure I have 

 found a difference in the negro as compared with the white brain. In the latter 

 it ascends as we have remarked, obliquely backward and upward; but in the 

 negro brain it assumes at its anterior portion a horizontal direction and the posterior 

 runs in a direction nearly perpendicular to this. This arrangement was also noticed 

 by Marshall in the brain of the Bushwoman, and it may also be seen in the figure 

 given by Gratiolet of the brain of the Hottentot Venus. 



The Sylvian fissure gives off at its anterior portion an ascending branch, A. S, 

 Plate XLI, fig. 1. This passes directly up into the frontal lobe and constitutes the 

 anterior boundary of the so-called operculum. This fissure has been considered by 

 Pansch, Bischoff, Ecker and others as a fundamental fissure. It is true that it 

 makes its appearance early in the history of human development, as may be seen 

 by comparing figures 8 to 16, Plate XXXV, but as Ave have already seen, it is 

 present as a well developed fissure only in Man and the Anthropomorpha. A slight 

 indication of it can also be seen in Cynocephalus, Plate XXXVIII, fig. 4, but in the 

 Primates in general there is no sign of its development, as may be noted by 

 examining figures on Plates XXXVII and XXXVIII. I do not, therefore, consider 



1 Comparative Anatomy of Vertebrates. 

 36 JOURX. A. X. S. PHILA.. VOL. X. 



