320 



MORPHOLOGY OF THE CEREBRAL CONVOLUTIONS. 



quently continuous with the fissura interparietalis, does not behave in the above- 

 mentioned manner, I believe I have proved by repeated observation. This furrow is 

 in the majority of seven months foetuses not yet visible. On the contrary, there is 

 such a fissure in the eighth and ninth month which does not again disappear. In 

 the fifth month, on the other hand, I have again and again, sometimes alone a,nd 

 sometimes present with other transverse furrows, often seen a deep entering fissure 

 pointed at both ends which corresponds exactly in its position with that mentioned 

 by Bischoff as running across the occipital lobe, and that this fissure later again dis- 

 appears is probably certain, for at this spot during the sixth and seventh month there 

 is generally no trace of such a fissure." 



With Ecker I have found in foetal brains the fissure which he terms the fissura 

 occipitalis transversus well developed and not disappearing, but fully represented in 

 adult human brains. It is represented in figs. 8, 10, 12, 14 and 16, PI. XXXV, and 

 figs. 1 and 3, PI. XXXVI. It represents the external perpendicular of the apes, 

 which has been thrust backward and variously contorted by the increased convolu- 

 tional development taking place in this region in the higher Primates including Man. 

 It is the fissure marked o 1 , in figs. 5 and 6, PI. XXXVI, and fig. 1, PI. XL. It may 

 be seen by studying these figures that the external perpendicular fissure is separated 

 from the internal by the development of the convolution, 2, upward from its floor. 

 The simpler, and in this respect more ape-like character of the negro brain, renders 

 the true nature of this change as found in the human brain very evident. Fig. 5, 

 PL XXXVI, is from the occipital lobe of the brain represented in fig. 1, PI. XLII, 

 whilst fig. 6, PI. XXXVI, is a posterior view of the mulatto's brain of fig. 1, PL 

 XLIV. 



Marshall, as we have already seen, calls the lateral portion of the parieto- 

 occipital the external perpendicular ; but this is, as we now see, only the upper end 

 of the fissura perpendicularis interna. The external is really the fissure marked o 1 , 

 the fissura occipitalis transversus of Ecker and more recent writers ; and the condi- 

 tion of things in the Anthropomorpha, Ateles, Hylobates, and in the brain of Man, 



is produced in the following man- 

 ner : In most of the monkeys, 

 such as Cefois, Cercopithecus, 

 Macacus, Cynocephalus, etc., we 

 will find on looking directly down 

 upon the hemisphere the fissures 

 arranged as in the diagrams, figs. 

 18 and 19, where AB represents 

 the line of the longitudinal fissure 

 separating the two hemispheres 

 from each other, i p, the interpa- 

 rietal fissure ; O 1 , the external 

 perpendicular, PO, the parietal- 

 occipital. P 1 and P 2 are respect- 



Fig. 18. 



Fig. 19. 



