114 JiECTURE IV, 



convolutions of the posterior lobe. The three other transition 

 convolutions of Gratiolet are included by Wagner in the middle 

 story {(P) ; and he also distinguishes beneath this a third, but 

 not distinctly developed story [d?), which rests immediately 

 upon the cerebellum. 



Gratiolet, by extending his observation to the brains of apes, 

 has shown the special importance of these transition convolu- 

 tions. In these animals, in consequence of the greater depth 

 of the perpendicular fissure, the anterior border of the pos- 

 terior lobe becomes gradually a flap which, by overlapping the ^ 

 parietal lobe, covers more or less the transition convolutions. 

 This flap, which, in its inner surface, has a very characteristic 

 structure, must be lifted back in order to see these transition 

 convolutions in the closed fissure into which they seem to have 

 sunk. Gratiolet has even attempted to advance this formation 

 as a peculiar characteristic, distinguishing the simian from the 

 human brain. He, however, omitted to take into consideration 

 that the formation of this flap increases in the ape but very 

 gradually ; that the plis de passage are very inconstant, fre- 

 quently difiering on both sides, so that, according to another 

 observer, if we merely keep in view the arrangements of these 

 convolutions, the two hemispheres might belong to difierent 

 species ; and finally, that there are apes in which all transition 

 convolutions lie as much on the surface as in man, and which 

 would, therefore, have to be considered as human, if these 

 convolutions were really indicative of the human character. 

 These apes are, according to Gratiolet^s own observations, the 

 Ateles which stand next to the howling monkeys. 



For the better understanding of the discussions on the dis- 

 tinction between man and ape, I must allude to some points 

 regarding the minute structure of the brain which have re- 

 cently gained a special importance. 



As already mentioned at the beginning of this lecture, the 

 hemispheres are developed from the brain-trunk by arches 

 which, at first, proceed along the parietes of the skull and 

 deposit substance internally, until both parts, the brain-trunk 

 and the brain-vault, are so connected that only a system of 

 cavities, remains, which cavities have received the name of 

 ventricles. 



