to fall on one side and roll rapidly on its longitudinal axis. According to Schiff, if the peduncle be divided from behind, the animal falls on the same side as the injury; if the section be made in front, the animal turns to the opposite side.

Disease of the cerebellum partially corroborates the result of experiments; in many cases symptoms of unsteadiness of gait, from a want of coördination, have been noticed.

Comparative anatomy reveals a remarkable correspondence between the development of the cerebellum and the complexity of muscular actions. It attains a much greater development, relatively to the rest of the brain, in those animals whose movements are very complex and varied in character, such as the kangaroo, shark, and swallow.

The cerebellum may possibly exert some influence over the sexual function, but physiological and pathological facts are opposed to the idea of its being the seat of the sexual instinct. It appears to be simply a center for the coördination and equilibration of muscular movements.

CEREBRUM.

The Cerebrum is the largest portion of the encephalic mass, constituting about four-fifths of its weight; the average weight in the adult male is from 48 to 50 ozs., or about three pounds, while in the adult female it is about five ozs. less. After the age of forty the weight of the cerebrum gradually diminishes at the rate of one ounce every ten years. In idiots the brain weight is often below the normal, at times not amounting to more than twenty ounces.

The Blood Supply to the cerebrum is unusually large, considering its comparative bulk, nearly one-fifth of the entire volume of blood being distributed to it by the carotid and vertebral arteries. These vessels anastomose so freely, and are so arranged within the cavity of the cranium, that an obstruction in one vessel will not interfere with the regular supply of blood to the parts to which its branches are distributed. A diminished amount, or complete cessation, of the supply of blood is at once followed by a suspension of its functional activity.

The cerebrum is connected with the pons Varolii and medulla oblongata through the crura cerebri, and with the cerebellum through the superior peduncles. It is divided into two lateral halves, or hemispheres, by the longitudinal fissure running from before backward in the median line; each hemisphere is composed of both white and gray matter, the former being

internal, the latter external; it covers the surfaces of the hemisphere which are infolded, forming convolutions, for economy of space.

Fissures.

1. The fissure of Sylvius is one of the most important; it is the first to appear in the development of the fetal brain, being visible at about the third month; in the adult it is quite deep and well marked, running from the under surface of the brain upward, outward, and backward, and forms a boundary between the frontal and temporo-sphenoidal lobes.

2. The fissure of Rolando is second in importance, and runs from a point on the convexity near the median line transversely outward and downward toward the fissure of Sylvius, but does not enter it. It separates the frontal from the parietal lobe.

3. The parietal fissure, arising a short distance behind the fissure of Rolando, upon the convexity of the hemisphere, runs downward and backward to its posterior extremity.

4. The parieto occipital fissure, separating the occipital from the parietal lobes. Beginning upon the outer surface of the cerebrum, it is continued on the mesial aspect downward and forward until it terminates in the calcarine fissure.

5. The calloso-marginal fissure lying upon the mesial surface, where it runs parallel with the corpus callosum.

Secondary fissures of importance are found in different lobes of the cerebrum, separating the various convolutions. In the anterior lobe are found the pre-central, superior frontal, and inferior frontal fissures; in the temporo-sphenoidal lobes are found the first and second temporosphenoidal fissures; in the occipital lobe, the calcarine and hippo-campal fissures.

Convolutions. Frontal lobe.

The ascending frontal convolution, situated in front of the fissure of Rolando, runs downward and forward; it is continuous above with the anterior frontal, and below with the inferior frontal convolution.

The superior frontal convolution is bounded internally by the longitudinal fissure, and externally by the superior frontal fissure; it is connected with the superior end of the frontal convolution, and runs downward and forward to the anterior extremity of the frontal lobe, where it turns backward, and rests upon the orbital plate of the frontal bone.

The middle frontal convolution, the largest of the three, runs from behind forward, along the sides of the lobe, to its anterior part; it is bounded above by the superior and below by the inferior frontal fissures.