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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 photographs 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 Mémoire sur les Plis Cérébraux de 1' Homme et des Primatés, so often referred to.
Fig. 1, is a lateral view of the brain of the orang. It shows the following points:—
i. The even curve described by the superior boundary line of the hemispheres.
ii. The vertical direction of the fissure of Sylvius, F.
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.
Fig. 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 hemispheres.
Fig. 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 cerebrum. 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 being 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.
