Page:Natural History Review (1861).djvu/215

Rh power of discovering the third class of differences, we are indebted to M. Gratiolet's masterly analysis of the cerebral convolutions. Previously to the appearance of the "Memoire sur les Plis Cerebraux de 1' homme et des Primatès," it was all but impossible to express in words the differences which the eye detected in the arrangement in two different brains of what has been called "the chaos of the convolutions." What was previously all but an impossibility, M. Gratiolet's philosophy has made an easy task. No apology can be necessary for adopting his phraseology, as the right of naming the country he has conquered, is a prerogative never denied to one, who has succeeded in subduing a territory which few before him had even thought of invading.

Under our fourth head we shall arrange those points of difference which a dissection of the brain alone can reveal.

These four heads correspond, it is obvious, to the successive stages of an anatomical investigation; and they possess, consequently, the merit not merely of colligating conveniently the results, but also of corresponding accurately to the several processes of an accurate anatomical investigation.

The orang dissected was a young male (Simia Morio). The first two molars had just come into use in both jaws; the weight of the entire body was but 16 lbs. 12 oz.; the height was 2 feet 7 inches. None of the internal viscera presented any appearance of disease. The lungs, which were both but unilobar, were crepitant throughout, free from congestion, collapse, or tubercle. The callosities on the backs of the fingers, which have been held, and with some show of probability, to indicate the existence of a state of debility, were absent.

The roof of the cranium was removed by a circular incision, intersecting the foramen magnum posteriorly. Before the removal of the dura mater, the cerebral hemispheres were seen to cover the superior surface of the cerebellum entirely, and even to project a very little way beyond it, posteriorly. After the removal of the dura mater, a small segment of cerebellar surface became visible on each side, posteriorly to the tips of the occipital lobes. It is well known that the anteroposterior dimensions of the corpus callosum are very different in a brain whilst contained and supported within its case, and when removed from the skull,—the forward swaying of the hemispheres upon their supporting stems, the crura, flattening the previously arched commissure. That it was the weight of the hemispheres, working similarly, which produced the alteration just noted in the relations of the cerebrum to the cerebellum was seen thus'—A wider segment of cerebellar surface was visible on the left side than on the right, the animal lying over towards its right side.