LECTURE IV. 113 



which is mostly only seen in a side view of the brain, usually 

 joins a curve, like a bent finger, around the parallel fissure, 

 which will be mentioned further on when speaking of the tem- 

 poral region, whence Gratiolet calls it the bent convolution, 

 pli courbS. 



The third, or lower parietal convolution {b^), generally ap- 

 pears in the shape of a triangular knob, wedged in between 

 the branches of the horizontal arm of the Sylvian fissure, and 

 corresponds in its position pretty nearly to the parietal emi- 

 nence of the skull. 



The convolutions of the temporal lobe are generally simple, 

 and can only be distinctly seen in a side view. The superior 

 edge of the lobe, as already observed, is bounded by the hori- 

 zontal branch of the Sylvian fissure. On the lobe, parallel 

 with this, there is a fissure — the parallel fissure (P. 8.) — which 

 stretches far back towards the posterior lobe and the perpen- 

 dicular fissure, and separates the upper story of the temporal 

 convolutions (c^) from the intermediate (c"). A second smaller 

 furrow separates the middle story from the lower {r?), which 

 rests on the base of the skull. In poorly convoluted brains, 

 these stories are scarcely at all notched on their margins ; but 

 in richly convoluted brains, the notches become secondary 

 fissures, which, however, are rarely sufficiently deep to efiace 

 the original tripartition of the lobe. 



The occipital lobe seems, in every respect, the most difiicult 

 as regards the systemisation of its convolutions. As in the 

 human brain, its limit is only indicated by a very small per- 

 pendicular fissure, it runs without any visible separation into 

 the parietal and temporal lobes. It is, moreover, very small, 

 the convolutions are mostly very irregular and unsymmetrical ; 

 whilst, on the contrary, in the ape it is well defined by the 

 great development of the perpendicular fissure. 



On the margins of the lobes, Gratiolet distinguishes four 

 so-called transition convolutions [plis de passage), of which 

 the first, or upper — which Wagner calls the first convolution of 

 the posterior lobe {cl^), adjoining the central line, behind the 

 first parietal convolution — sends forth some folds towards the 

 posterior lobe, which Grratiolet terms the upper story of the 



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