312 ORIGINAL ARTICLES. 



area of the longitudiually divided corpus callosum iu the Chimpanzee, 

 is therefore f-f^ths of a square inch ; whilst in man it is U2_o_9ths of a 

 square inch. Comparing these numbers with the area of the internal 

 surface of one of the cerebral hemispheres, in the Chimpanzee's and 

 in the human brain, we find them to be as 1 to 28*5 in the ape, and 

 1 to 12 - 5 in man ; so that the corpus callosum is more than twice as 

 large, proportionally to the size of the brain, in man, as it is in the 

 Chimpanzee. We may add, that the corpus callosum in our specimen 

 is exactly of the same length as in Schroeder van der Kolk's figure, 

 whilst the brain itself is a little longer. As in man, the corpus 

 callosum of the ape, is thickest behind. The section of the anterior 

 commissure is not so round as in the human brain, but it is propor- 

 tionally as large. The posterior commissure also exists, but it is 

 small. The so-called soft commissure is large. On the whole then, 

 the system of transverse commissural fibres is defective in the Chim- 

 panzee, as compared with man ; and as the section of the medulla 

 oblongata, hi the former, is even larger in proportion to the cerebrum, 

 than in the latter, it would seem as if the relative deficiency of white 

 substance within the hemispheres, already noticed, is, to a great degree, 

 owing to the fewness of these, as well as other, commissural fibres. 

 Of the longitudinal system of commissures, the fornix is thin ; the 

 taenia semicircularis is only just recognisable ; and the striae longitu- 

 dinales are slender. 



Of the middle and fifth ventricles, nothing is to be remarked. 

 The fourth is very wide, corresponding in this respect with the cere- 

 bellum. The lateral ventricle, examined on the right hemisphere, 

 proved to be a very large cavity. It consisted, as in man, of a body 

 (fig. 5), ## and three cornua ; an anterior cornu # , a descending 

 cornu (of which only the commencement is seen) ; and a very 

 obvious, posterior cornu. * * * The body measured 12/10ths of 

 an inch long, the anterior cornu 6/10ths, the posterior cornu 

 nearly 5/10ths, and the descending cornu 20/10ths ; whereas in the 

 human brain, these parts measured respectively, 21/10ths, 14/10ths, 

 12/10ths and 26/10ths of an inch. Comparing these dimensions 

 with the lengths of the two brains, (44/10ths, and 65/10ths of an inch) 

 we get as ratios for the Chimpanzee, "207, '103, *18 and -45 to 1, 

 and for man, '32, -21, "184 and '4 to 1. From this we perceive that 

 the lateral ventricle was proportionally longer in the human brain, 

 except as regards the descending cornu ; and that the posterior 

 cornu was only fractionally longer. It is worthy of note, as may 

 be seen by comparing the dissected with the undissected side of fig. 

 5, that, in the ape, the body of the lateral ventricle corresponds 

 almost exactly with the parietal lobe of the hemisphere, P, whilst the 

 anterior cornu projects into the frontal lobe, F, and the posterior 

 runs, beyond the vertical fissure, into the occipital lobe, O : the de- 

 scending cornu of course occupies the temporo-sjohenoidal lobe, 

 Fig. 4, T. In the human brain, the same relations are observed, 

 together with a coincidence in the measurements of the parts. In 

 our Chimpanzee's brain, the posterior cornu begins at a line, midway 



