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Proceedings of the Royal Society 
the quadrate lobule, and the inferior annectent gyrus, and poste- 
riorly it turned round the upper branch of the sulcus, and joined 
the supero-occipital gyrus. The collateral sulcus (n n) reached 
almost the entire length of the tentorial aspect of the hemisphere, 
and although neither so deep, nor extending so far back as the 
calcarine sulcus, yet reached in front almost as far as the tip of the 
temporo-sphenoidal lobe. Some small secondary fissures proceeded 
from it. The internal occipital (25) and quadrate (18') lobules were 
well seen, and the latter was considerably larger than the former. 
The three specimens of the brain of the Chimpanzee just described 
prove that the generalisation which G-ratiolet has attempted to 
draw of the complete absence of the first connecting 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 specimen did the brain, in these particulars, 
follow the law which G-ratiolet has expressed. As regards the 
presence of the superior bridging convolution, I am inclined to 
think that it has 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 much less frequent, and has as yet, I 
believe, only been seen in the brain (A) recorded in this communi- 
But few specimens of the brain of the Chimpanzee have as yet been 
figured or described. In that figured by Tyson, only the base and an internal 
view of the brain are given. In the brains figured and described by Gratiolet, 
and Van der Kolk and Vrolik, and in my brain (C) no superior bridging con- 
volution existed. In the brains described by Kolleston and Marshall, as well 
as in the brains A and B now described, it is precisely stated that it was pre- 
sent in one hemisphere. In the brain figured by Tiedemann (PA^7. Trans. 
1836), from a specimen in the Hunterian Museum, London, it is apparently 
present in the left hemisphere, though it is not referred to in the description ; 
and from the drawing of a careful cast of the brain dissected by Dr Macartney 
{Trans. Royal Irish Acad. 1843), it seems probable that the first bridging 
convolution existed in his specimen. 
Addendum, May 5 . — Since the above paper was read, a fine young male 
Chimpanzee has been purchased by Professor Goodsir for the Anatomical 
Museum, the brain of which I removed and examined. In both hemispheres 
the parieto-occipital fissure was unbridged, and the opercular edge of the 
occipital lobe was as sharp andwell defined as in my brain (C), or in the speci- 
men figured by Gratiolet. 
