Page:Popular Science Monthly Volume 26.djvu/755

Rh and enlargement of the spinal-cord; above this we see the pons Varolii, and to right and left the lobes of the cerebellum which lie under the posterior portions of the cerebrum. At the upper part of the pons we see two stems or crura passing to the cerebrum, and serving to join that larger organ with the nerve-matter below.

A little above the crura, and near the center of the mass, we see what is called the

optic commissure. This is simply the crossing of the optic nerves on their way to the eyes. Directly below this commissure are two small rounded eminences called the corpora albicantia, while above, on a stem, is the pituitary body. Beyond the optic commissure lie the olfactory bulbs, one on each hemisphere, placed in a slight depression of the surface. If we turn the brain over, its numerous convolutions are seen extending from end to end, from side to side, and also following the lateral surfaces right and left of the great longitudinal fissure.

On removing a horizontal piece from the upper portion of each hemisphere, the cell-matter of the surface will be found to follow the different windings, while the center of each convolution will be seen to be made up of fibers continuous with fiber-matter in the interior of the hemisphere. Should we cut deeper, we would come upon the corpus callosum, the band of connection between the hemispheres; this body is