216 ORIGINAL ARTICLES. 



Description of Plates. 



These four views of the brain of the orang are copies of photographs 

 taken of it by Messrs. Hills and Saunders, of Oxford. The brain had been 

 carefully hardened in spirit for as much as two months before it was thus 

 photographed. The figures are numbered in the order in which the pho- 

 tographs were taken. The numbers placed upon the convolutions on the 

 exterior surface of the brain will be found to correspond with those 

 similarly employed by M. Gratiolet in his invaluable Memoire sur les 

 Plis Cerebraux de 1' Homme et des Primates, so often referred to. 



Fig. 1, is a lateral view of the brain of the orang. It shows the fol- 

 lowing points : — 



i. The even curve described by the superior boundary line of 

 the hemispheres. 



ii. The vertical direction of the fissure of Sylvius, P. 



iii. The failure of the posterior lobes to cover the cerebellum 

 entirely. 



iv. The diminished downward growth of the posterior lobes, as 

 shown by the obliquity of a line drawn along their surface 

 where it lies upon the cerebellum, C. 



v. The presence of the outer part of the lateral vertical fissure, 

 which outer part is always filled up in man, even when 

 the inner may not be so, as the inner is in the orang. 

 Pig. 2 is a basal view of the same brain. It shows the following 

 points : — 



i. The great relative thickness of the nerves to the mass of the 

 brain. 



ii. The absence of any marked excavation of the orbital lobes. 



iii. The lateral and posterior development of the cerebellar he- 

 mispheres. 

 Pig. 3 represents the brain of the orang as seen from above. It shows 

 the following points : — 



i. The greater extent to which the cerebellum has come into view 



on the left side than on the right. 

 ii. The want of symmetry between the two sides of the cere- 

 brum. The longitudinal fissure seems on the left to be 

 bounded by a continuous vertically unindented table-land, 

 on the right by a table-land indented at two points. The 

 posterior of these two points corresponds to the external 

 vertical fissure, the first or superior pli de passage a, a be- 

 ing partially concealed under the operculum, and allowing 

 us thus to mark off the occipital from the principal lobes 

 nearly as sharply as in the Chimpanzee. The three frontal 

 convolutions, 1 , 2, 3 ; the two ascending parietals, 4, 5, 

 and the lobule of the second ascending convolution, 5', are 

 asymmetrical on the two sides of the brain. 



