assume a position nearly parallel to the under surface of the brain, instead of descending obliquely from it; hence, the cerebellum falls backwards further than in its natural state, presses somewhat aside the posterior ends of the cerebral hemispheres, and so modifies the proper relative position of these parts of the encephalon. Besides this, the general subsidence of the cerebral hemispheres, the falling asunder of the points of the middle lobes, and the sinking in of the cerebellum between the hinder portions of the cerebrum, diminish the concavity of the orbital surfaces, injure the concave outline of the lower border of the posterior half of the hemisphere, and convert its natural overhanging curve into a nearly even, oblique border, passing backwards and upwards, above the cerebellum. All these changes, which must be still more marked in brains already partially decomposed, will be better appreciated by comparing the photographic illustrations of our Chimpanzee's brain given in Plate VI. figs. 2 and 4, with the outlines, figs. 1 and 3, (also taken from photographs) of a plaster cast, which I made of the interior of the cranium of the animal, before the dura mater was removed from the bone, and in which, the divided tentorium was first carefully stitched up, on both sides.
A comparison of these figures is of great interest, for it will not only serve to elucidate a subject of controversy, just now of importance, but it will demonstrate conclusively, that no proper estimate of the general form of the encephalon, either of man or of brutes; no exact measurements of its parts; and no correct idea of their mutual positions, can be obtained, unless by hardening the brain before it is removed, or by correcting the notions derived from an examination of this otherwise flaccid organ, by constant reference to the internal form of the cranial cavity in which it was contained. M. Gratiolet has been well aware of this fact and has availed himself of it in his valuable researches; but he has left an abundant field for future observation. The internal forms of the crania of the different races of mankind, especially, need to be systematically investigated and measured in a similar manner.
The illustrations which accompany this Paper will enable the reader to follow me, in the critical examination which I here feel called on to make, of the various original representations of the Chimpanzee's brain given by Tyson,[1] Tiedemann,[1] Macartney,[1] Schroeder van der Kolk and Vrolik,[1] and Gratiolet.[1] Tested by a comparison with the brain and cranial cast in my possession, or (as the reader must do) with the faithful facsimiles of those objects taken by aid of photography, the figures given by these authors will all be found to exhibit, unmistakeably, the Chimpanzee characters; but they differ materially in value.
Tyson's figures are useless for modern science—in the main, owing to their want of artistic rendering; the basal view, as shown by the position of the curved supra-orbital borders, is taken too much
