fested, as after a section of one crus cerebri, which, however, may be due to giddiness and loss of sight.

They also assist in the coördination of the complex movements of the eye, and regulate the movements of the iris during the movements of accommodation for distance.

CORPORA STRIATA AND OPTIC THALAMI.

The Corpora Striata are two large ovoid collections of gray matter, situated at the base of the cerebrum, the larger portions of which are imbedded in the white matter, the smaller portions projecting into the anterior part of the lateral ventricle. Each striated body is divided, by a narrow band of white matter, into two portions, viz.:—

1. The caudate nucleus, the intraventricular portion, which is conical in shape, having its apex directed backward, as a narrow, tail-like process. 2. The lenticular nucleus, imbedded in the white matter, and for the most part external to the ventricle; on the outer side of the lenticular nucleus is found a narrow band of white matter, the external capsule; and between it and the convolutions of the island of Reil, a thin band of gray matter, the claustrum; the corpora- striata are grayish in color, and when divided present transverse striations, from the intermingling of white fibers and gray cells.

The Optic Thalami are two oblong masses situated in the ventricles posterior to the corpora striata, and resting upon the posterior portion of the crura cerebri. The internal surface projecting into the lateral ventricles is white, but the interior is grayish, from a commingling of both white fibers and gray cells. Separating the lenticular nucleus from the caudate nucleus and the optic thalamus is a band of white tissue, the internal capsule.

The internal capsule is a narrow, bent tract of white matter, and is, for the most part, an expansion of the motor tract of the crura cerebri. It consists of two segments, an anterior, situated between the caudate nucleus and the anterior surface of the lenticular nucleus, and a posterior, situated between the optic thalamus and the posterior surface of the lenticular nucleus. These two segments unite at an obtuse angle, which is directed toward the median line. Pathological observation has shown that the nerve fibers of the direct and crossed pyramidal tracts can be traced upward through the anterior two-thirds of the posterior segment, into the centrum ovale, where, for the most part, they are lost; a portion, however, remain

ing united, ascend higher and terminate in the paracentral lobule, the superior extremity of the ascending frontal and parietal convolutions. The sensory tract can be traced upward, through the posterior third, into the cerebrum, where they probably terminate in the hippocampus major and unciate convolution.

Functions. The corpora striata are the centers in which terminate some of the fibers of the superficial or motor tract of the crura cerebri; others pass upward through the internal capsule, to be distributed to the cerebrum. It might be inferred, from their anatomical relations, that they are motor centers. Irritation by a weak galvanic current produces muscular movements of the opposite side of the body; destruction of their substance by a hemorrhage, as in apoplexy, is followed by a paralysis of motion of the opposite side of the body, but there is no loss of sensation. When the hemorrhagic destruction involves the fibers of the anterior twothirds of the posterior segment of the internal capsule, and thus separates them from their trophic centers in the cortical motor region, a descending degeneration is established, which involves the direct pyramidal tract of the same side and the crossed pyramidal tract of the opposite side.

Destruction of the posterior one-third of the posterior segment of the internal capsule is followed by a loss of sensation on the opposite side of the body, and a loss of the senses of smell and vision on the same side (Charcot). The precise function of the corpora striata is unknown, but they are in some way connected with motion.

The optic thalami receives the fibers of the tegmentum, the posterior portion of the crura cerebri. They are insensible and inexcitable to direct irritation. Removal of one optic thalamus, or destruction of its substance by disease or hemorrhage, is followed by a loss of sensibility of the opposite side of the body, but there is no loss of motion; their precise function is also unknown, but in some way connected with sensation. In both cases their action is crossed.

CEREBELLUM.

The Cerebellum is situated in the inferior fosse of the occipital bone, beneath the posterior lobes of the cerebrum. It attains its maximum weight, which is about 5 ozs., between the twenty-fifth and fortieth years, the proportion between the cerebellum and cerebrum, being 1 to 84.

It is composed of two lateral hemispheres and a central elongated lobe, the vermiform process; the two hemispheres are connected with each other by the fibers of the middle peduncle forming the superficial portion of the

pons Varolii. It is brought into connection with the medulla oblongata and spinal cord through the prolongation of the restiform bodies; with the cerebrum, by fibers passing upward beneath the corpora quadrigemina and the optic thalami, and then forming part of the diverging cerebral fibers.

Structure. It is composed of both white and gray matter, the former being internal, the latter external, and convoluted, for economy of space.

The White matter consists of a central stem, the interior of which is a dentated capsule of gray matter, the corpus dentatum. From the external surface of the stem of white matter processes are given off, forming the lamina, which are covered with gray matter.

The Gray matter is convoluted and covers externally the laminated processes; a vertical section through the gray matter reveals the following

structures:

I. A delicate connective tissue layer, just beneath the pia mater, containing rounded corpuscles, and branching fibers passing toward the external

surface.

2. The cells of Purkinje, forming a layer of large, nucleated, branched nerve cells sending off processes to the external layer.

3. A granular layer of small, but numerous corpuscles.

4. Nerve fiber layer, formed by a portion of the white matter.

Properties and Functions.-Irritation of the cerebellum is not followed by any evidences either of pain or convulsive movements; it is, therefore, insensible and inexcitable.

Co-ordination of Movements.-Removal of the superficial portions of the cerebellum in pigeons produces feebleness and want of harmony in the muscular movements; as successive slices are removed, the movements become more irregular, and the pigeon becomes restless; when the last portions are removed, all power of flying, walking, standing, etc., is entirely gone, and the equilibrium cannot be maintained, the power of coördinating muscular movements being entirely gone. The same results have been obtained by operating on all classes of animals.

The following symptoms were noticed by Wagner, after removing the whole or a large part of the cerebellum. I. A tendency on the part of the animal to throw itself on one side, and to extend the legs as far as possible. 2. Torsion of the head on the neck. 3. Trembling of the muscles of the body, which was general. 4. Vomiting and occasionally liquid evacua

tions.

Forced Movements.-Division of one crus cerebelli causes the animal