MARSHALL ON THE BRAIN OF A YOUNG CHIMPANZEE. 307 



margins of those bones, we find that the proportionate dimensions 

 in the Chimpanzee would be 46, 28, 26, instead of 54, 23, 23, out of 

 100, as in man. 



Turning next to the outer side of the cerebral hemisphere, fig. 4, 

 the so-called parallel fissure, situated parallel with and behind, 

 the Sylvian fissure, is rather more complicated in our specimen 

 than in M. Gratiolet's figure. On the inner surface of the hemis- 

 phere, besides the internal perpendicular fissure, there is seen a 

 longitudinal fissure, surmounting the convolution of the corpus cal- 

 losum. And lastly, on the under surface, rather than on the 

 internal surface, of the hinder part of the hemisphere, is seen, very 

 well marked, the fissure of the hippocampus, commencing, as described 

 by Gratiolet, along the outer or lower border of the fimbriated con- 

 volution, and passing backwards in a curved direction, towards the 

 hinder extremity of the hemisphere. The corresponding fissures 

 plainly exist in the human brain dissected by us, pari passu with that 

 of the Chimpanzee. 



Now, whatever grounds of definition as to the leading sub-divi- 

 sions of the cerebral hemispheres may be adopted, it is at once 

 apparent that all those sub-divisions of the human cerebrum, called 

 lobes, are present in the Chimpanzee. In the phraseology of the 

 older anatomists, the anterior and middle lobes are well distinguished 

 by the fissure of Sylvius, which, however, is comparatively not qrrite so 

 deep as in man. At the bottom of this fissure, is plainly seen the insula, 

 or island of Eeil. Looking at the Chimpanzee's brain, it is quite indif- 

 ferent whether we choose the usual arbitrary definition of the limits 

 between the middle and posterior lobe, viz., a line drawn in front of 

 the cerebellum, or whether we select the one more recently laid down, 

 according to which the posterior lobe signifies that part " which covers 

 the posterior third of the cerebellum and extends beyond it" ;* for, 

 in either sense, the posterior lobe exists in our Chimpanzee's brain, 

 inasmuch as the cerebrum projects half an inch beyond the cerebellum 

 in its natural and undisturbed position, whilst the human cerebrum, 

 under the same conditions, projects only a tenth of an inch more. 



If, however, we reject these arbitrary modes of distinguishing the 

 various lobes, and follow a more philosophical method, for example, 

 the one suggested by Gratiolet, a corresponding conclusion is forced 

 upon us, viz., that all the great masses in the human brain have their 

 anatomical representatives, or homologues, in the Chimpanzee. The 

 frontal lobe (figs. 4 and 5) F, together with the parietal lobe P, 

 marked off by the first ascending convolution 4 » 4 '» which is included in 

 the latter, lie above the Sylvian fissure, and in front of the vertical 

 or perpendicular fissure; the teviporo-sphenoidal lobe, T, lies below the 

 Sylvian fissure ; the central lobe is the island of Eeil ; and the occi- 

 pital lobe, O, is the part behind the external vertical fissure. Though 

 this latter fissure is broken across by convolutions, its place can 



* Professor Owen. 



