304 ORIGINAL ARTICLES. 



tive ividtli, — as shown by measurements taken in its natural state and 

 position, not when it is disturbed and displaced, — a statement some- 

 what differing from that usually made. In the Chimpanzee, propor- 

 tionally less of the under surface of the cerebrum is seen on each side 

 of the cerebellum, than in man ; but posteriorly, though the area of 

 cerebral surface seen, is less in this animal than in man, yet the 

 antero-posterior measurement of the surface is, in proportion to that 

 of the entire brain, greater in the Chimpanzee, being about ith of the 

 total length of the cerebrum, and, we may add, -ith the distance 

 from the point of the middle lobe to the posterior end of the cere- 

 brum, instead of T x r th and -|th respectively, as in man. As to the 

 medulla oblongata, it is less fore-shortened in this basal view of the 

 Chimpanzee's brain, than in man's, because it inclines a little more 

 backwards. In harmony with Soemmerring's law, the width of the 

 medulla at its base is, proportionately to that of the cerebrum, wider 

 in the Chimpanzee's, than in the human, brain. 



If, finally, we take as a sort of arbitrary central point for the 

 entire cerebral mass, the centre of its common stalk, the medulla oblon- 

 gata, where it intersects the pons ; and imagine lines drawn thence to 

 the extreme occipital, frontal, parietal and vertical points of the 

 cerebrum, we find that, in the Chimpanzee, the actual lengths of 

 those cerebral radii, as they might be called, are respectively, 23, 29, 

 26, and 29 tenths of an inch, whereas, in man, they are 33, 43, 39 

 and 46 tenths of an inch. These numbers show, not only, the abso- 

 lutely, far greater size of the human cerebrum, but taking its size 

 as the standard, they show that the deficiency of the Chimpanzee's 

 cerebrum, is most marked in the vertical radius, next in the parietal, 

 then in the frontal, and least of all, in the occipital. In other words, 

 the superiority of development of the human cerebrum follows the 

 same order, as to regions, — being greatest in the vertical and parietal 

 combined, next in the frontal, and least of all, in the purely occipital 

 regions. The numerical ratios of these and other measurements will 

 be found in the following Tables. In Table I. the ratios are given in 

 reference to the human measurements as units ; a plan which I can- 

 not but think is preferable to that of making every separate animal's 

 brain a separate unit of comparison with man's. 



Table I. 



Measurements of the parts of the Encephalon in Man and the 

 Chimpanzee, given in -^ths of an English inch, with the ratios be- 

 tween them, taking the human measurements as units. 



Cerebrum. 



a. Extreme breadth , . .in Man 50, in Chimpanzee 37 = 1 to *74 



b. if length .... // 65 // 44 = 1 to -68 



c. // height .... // 45 // 29 = 1 to '65 



d. Length of orbital surface . . // 23 // 15 = 1 to *65 



e. Extreme depth of frontal lobe . // 35 // 20 ] to '57 



