FIG. 7.-Median surface of the cerebral hemisphere (after Ecker): Ipre, paracentral lobule (leg-center); sprc, paracentral sulcus: sc, extremity of the central sulcus; scm, callosomarginal sulcus; pc, precuneus; cu, cuneus; cc, corpus callosum; gu, uncinate gyrus; gh, hippocampal gyrus; af, fornicate gyrus; gd, descending gyrus, lingual lobule or lateral occipitotemporal gyrus: U, fusiform lobule or median occipitotemporal gyrus: Spo, parieto-occipital or occipital fissure; fca, calcarine fissure; fh, hippocampal

fissure.

center is encountered; and finally in the lowest portion of the socalled opercular area is the hypoglossal center (Fig. 8).

man.

Within the individual motor cortical centers smaller areas can be delimited for individual muscle-groups, whose situation in man also is known in part, because in operations upon the brain the surgeon is at times compelled to stimulate the cerebral cortex of the living human being with small electrodes of a faradic current in order to assure himself of the relations of the parts. The anterior and posterior central convolutions can be readily recognized upon the cerebral cortex by finding the two branches of the Sylvian fissure at the base of the brain. In the angle formed by the junction of these fissures the central sulcus or fissure of Rolando passes from the median fissure. In front of this is the anterior and behind it the posterior central convolution, which unite below in the lid or operculum (p. 29, Fig. 6).

Microscopic examination of the cerebral cortex shows that in the cortical motor centers are situated large ganglion-cells, which on account of their shape are designated pyramidal cells. These cells must be considered as the beginning of the motor or corticomuscular pyramidal tract. Each of these cells sends out an axis-cylinder process, which without division passes through the corona radiata, the internal capsule, the cerebral peduncle, the pons, and the medulla oblongata, to enter either the anterior pyramidal tract on the same side, or, after crossing over in the pyramidal decussation, the lateral pyramidal tract of the opposite side of the spinal cord. From this situation it enters the anterior gray matter of the spinal cord, and gives off numerous branches, which apply themselves to the branches of the large motor-trophic ganglion-cells in the anterior horns of the spinal cord, in order to convey motor impulses to the latter. Each pyramidal cell, with its axis-cylinder, to the spinal ramification, is designated a cerebrospinal neuron or a neuron of the second degree.

Paralysis and muscular twitching naturally occur if the motor pyramidal tract is interrupted or is irritated at any point in its course. In order to determine whether a paralysis is of cortical origin the following facts should be borne in mind:

Cortical paralysis not rarely occurs in the form of monoplegia, because the lesion has destroyed the functional activity of but a single cortical center. It is distinguished as central monoplegia from peripheral monoplegia by an absence of any alteration in the electric irritability and of degenerative muscular atrophy. On the other hand, muscular contractures and exaggeration of the tendonreflexes occur after a time, perhaps in consequence of secondary degeneration of the related pyramidal tracts.

In the course of diseases with a tendency to extension a cortical monoplegia may gradually be transformed into a cortical hemiplegia. Gradual development of hemiplegia is therefore indicative of cortical origin.

The mode of development of cortical hemiplegia is of diagnostie importance, because immediately adjacent cortical centers are involved successively. If, therefore, the arm-center is first attacked, involvement of the leg-center or of the facial center will next be superadded, and not that of the hypoglossal center, because it cannot readily be conceived that the facial center should thus escape. Cortical paralysis is not rarely attended with clonic spasm, less commonly with tonic spasm; and this is explained by assuming that not all of the pyramidal cells of a center are destroyed, so

that those that remain are irritated by the disease-focus and give rise to muscular contractions in the paralyzed members.

Cortical lesions that cause only irritation of the motor centers also induce only clonic muscular spasm. The cortical origin of such motor disturbances is indicated by persistent twitching of the same extremity. If, however, the clonic muscular contractions extend to adjacent motor centers-and this may be due to the remote action of even small foci of disease-the extension takes place in accordance with the anatomic relations of the individual centers, and intervening centers do not escape. In spite of general clonic muscular contractions consciousness is usually preserved. Under such circumstances the condition has been designated cortical or Jacksonian epilepsy.

The cortex of the frontal portion of the brain is associated with the processes of thought and of intelligence. In idiots the convolutions of the frontal region have been found but imperfectly developed. Perhaps disease of the gyrus rectus at the base of the brain is associated with alterations in character, and these may manifest themselves especially in a tendency to acts of violence. Lesions at the foot of the lorermost left frontal conrolution also known as the opercular portion of the inferior frontal convolution or as Broca's convolution, are of especial significance, as they cause motor (ataric) aphasia, which will be more fully discussed subsequently.

Little of a definite nature is known with regard to the finetions of the cortex of the parietal region. It is considered to be the cortical center for the muscular sense, so that patients whose cortex is destroyed in the parietal region have lost the power of determining the position of the extremities upon the opposite side of the body when the eyes are closed.

The cortex of the left temporal lobe, more accurately the posterior portion of the superior temporal convolution, contains the cortical radiation of the auditory nerve. Patients with destruction of this portion of the brain upon the left side suffer from word-deafness or sensory aphasia. Although they hear spoken words as sound, they are unable to comprehend and to utilize them. They are in the position of one hearing an unfamiliar and foreign language.

Injuries of the uncinate gyrus of the temporal portion of the brain (p. 31, Fig. 7) at the base of the brain are followed by disturbances in the sense of smell.

The occipital portion of the brain, finally, contains the cortical radiations of the optic-nerve fibers. Injuries of the cuneus and of the first occipital convolution (Fig. 7) are attended with hemianopsia (hemiopia).

The occurrence of hemianopsia may be explained as follows:

Within the chiasm of the optic nerves partial decussation of the fibers of these nerves takes place. At the same time the temporal portion of each

tract remains uncrossed, and only the fibers upon the nasal side undergo decussation (Fig. 9). Thus, for instance, the left optic tract supplies the temporal half of the left and the nasal half of the right retina." If, now, its cortical center in the left occipital lobe is destroyed, the power of vision is lost in the portions of the retina named, and the patient is incapable of seeing bodies brought toward him from the right. At times patients with injuries of the occipital cortex suffer from mind-blindness. They see objects, but do not recognize them, and they are incapable of comprehending what

FIG. 9.-Diagrammatic representation of the decussation of the optic fibers in the chiasm.

they see. If writing be not recognized, the condition is also spoken of as word-blindness. These conditions are associated with disease of the remainder of the occipital cortex with the exception of the cuneus.

FOCAL SYMPTOMS ATTENDING DISEASE OF THE CENTRUM

SEMI-OVALE.

Situated between the cerebral cortex and the basal ganglia of the brain are white medullated masses, known as the centrum semi-ovale. These contain association-fibers, which connect points in the cerebral cortex of the same hemisphere; commissural fibers, which, through the corpus callosum, connect symmetrical points in the cerebral cortex of each hemisphere; and fibers of the corona radiata. The latter includes those systems of fibers that penetrate from the cerebral cortex into the depth of the brain and establish a connection between the cortex and the surface of the body. As yet, no disturbances are known that indicate disease of the association-fibers and the commissural fibers. If, however, a lesion occurs in the corona radiata, the same symptoms appear as if the lesion

were situated in the related cortical area itself, and it is impossible to determine with certainty during life whether a cortical lesion is present or one in the corona radiata. Foci of the latter kind

FIG. 10.-Horizontal section through the cerebrum: ak, internal capsule; (vs), anterior limb; (hs), posterior limb; (kn), knee; lk, lenticular nucleus, with its three divisions: ne, caudate nucleus; tho, optic thalamus: cc, mammillary bodies; ack, external capsule; cl claustrum; Fac, facial fibers in the posterior limb of the internal capsule; Pyr, pyramidal fibers for the extremities; Sens, sensory tract.

are, however, extremely rare. Lesions of the corona radiata from the central convolutions give rise to paralysis, and lesions of that from the occipital region to hemianopsia, etc.