CONNECTIONS OF POST-OPTIC GANGLION.

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rigemina in frogs, fishes, and mammals, we are forced to the conviction that these ganglia are important factors in the exhibition of the physical evidences of painful sensations in general.

Danilewsky finds that modifications in the arterial pressure, associated with a slowing of the heart and amplification of the pulse-waves, follows electric stimulation of these ganglia, and Budge and Valentin claim to have created contractions of the stomach, intestine, and bladder in the same manner. I am inclined to doubt, however, if these phenomena are due to the local effects of such stimulation, because we

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know positively that electric currents are often widely diffused. They have been adduced, however, by Ferrier as proofs (not well established) of the relation of the optic lobes to the reflex manifestations of emotion. Fear is not uncommonly exhibited, as we know, by the human race as well as by some animals, by involuntary passage of the urine and fæces, and occasionally by vomiting.

The relation of the corpora quadrigemina to vision, as well as some other pathological and physiological facts of clinical interest, has been considered more fully in previous pages, to which the reader is referred.

THE GENICULATE BODIES.-These ganglia (Fig. 43) are considered by some authors as appendages to the optic thalami and the corpora quadrigemina, because they appear to be associated to a greater or less extent with the special sense of sight. Their situation furthermore supports the view of Meynert, that they are also ganglia of origin of fibers of the tegmentum.

In the external geniculate body the gray matter is arranged in lamina which present, in cross-sections made through its substance, a zigzag outline, as if the lamina had been crushed or folded together. The cells of this mass are large, granular, and pigmented.

The internal geniculate body is less intimately connected with the optic lobes and the fibers of the optic tract, as proved by the latest researches of Flechsig, Gudden, and Ganser. . Its gray matter is not arranged in the manner peculiar to its companion, although it is apparently traversed by fibers of the optic tract connected with both the natis and testis cerebri. The nerve cells of this body appear to effect a decided reduction in the number of fibers which pass through it.

Some of the optic fibers pass directly from the optic tract to the corpora quadrigeminum without any intervention of these ganglionic bodies, while a few of the innermost bundles of the optic tract become apparently intertwined with the outermost fasciculi of the crusta. Burdach thinks that he has traced a connection between these bundles and the sub

RED NUCLEUS AND PINEAL GLAND.

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stantia nigra of Soemmering. Meynert has not been able to confirm this view.

THE RED NUCLEUS OF THE TEGMENTUM.-This ganglionic mass has been discussed already in connection with the superior peduncle of the cerebellum, and will be again referred to when the cerebellum is described. It is shown in Fig. 43.

THE MAMMILLARY TUBERCLE (corpus albicans-bulb of the fornix). The situation of this body, as well as its method of formation, is shown in a preceding diagram (Fig. 37). Its structure has been discussed in connection with the third ventricle. It is classed by Meynert and others among the ganglia of origin of the tegmental fibers.

THE PINEAL GLAND. This body (the conarium), which resembles a fir-cone in shape, lies above and between the two upper quadrigeminal bodies (Fig. 37). It is often spoken of as the "hypophysis cerebri," although improperly so according to the view of Meynert. The opinion of Luys that this body is directly continuous with the gray lining of the third ventricle is opposed by Arnold, who claims to have demonstrated that it is separated from it by a medullary layer. Meynert regards it as one of the ganglia of origin of the tegmentum cruris, since it is connected with the crus by means of the posterior commissure. It is also connected with the medullary substance of the cerebral hemispheres by means of its peduncles.

The cells which are found within the gray substance of the pineal gland are of two sizes, one 15μ and the other 6μ in thickness. These cells are packed more closely than in the other cerebral ganglia.

The pedicle of the pineal gland (habenula) is believed by Meynert to be directly connected with the posterior commissure of the third ventricle, as well as with the fornix anteriorly..

In microscopic structure the pineal gland bears a resemblance to the anterior lobe of the pituitary body. A number of hollow follicles may be demonstrated within it, which are filled with epithelial cells, and a gritty matter-the so-called

acervulus cerebri or brain-sand. This sabulous material is also found upon the exterior of the gland and its peduncles. During the development of the brain the pineal gland appears as a hollow excrescence from the part destined to form the third ventricle. Subsequently, this diverticulum becomes cut off from the ventricle, and tubes develop within it. Finally, these tubes are seen to separate into isolated vesicles, which are, as a rule, spherical in shape.

THE ARCHITECTURE AND FUNCTIONS OF THE CEREBELLUM. The cerebellum or "hinder-brain" consists of two lateral hemispheres, joined together by an intermediate portion which is called, from a fancied resemblance to a worm, the "vermiform process." The peculiar appearance of this process is due partly to its shape and partly to transverse ridges and furrows which are very apparent. When the under surface of the cerebellum is examined, this process appears as a well-marked projection, the "inferior vermiform process." On the upper surface it is only slightly elevated, forming the so-called "superior vermiform process." In birds, as well as in some animals lower in the scale, the vermiform process alone exists.' It is the part first developed in mammals. In most mammals, moreover, it constitutes a distinct central lobe, clearly demarkated from the lateral portions-the hemispheres of the cerebellum.

The cerebellar hemispheres are separated behind by a deep notch. Below, a deep fossa (the vallecula), which is continuous with the notch seen posteriorly, lodges, the inferior vermiform process. This hollow also receives the medulla in front, and the falx cerebelli behind. The hemispheres are convex on their lower surface, and tend to partly conceal the inferior vermiform process; above, however, they are somewhat flattened in the center, and slope downward toward the sides,

1 The vermiform process appears to be a complete ganglion in itself, associated with its own nerve tracts. The cerebellar hemispheres are added, in the higher grades of animals, in proportion to the development of the cerebral lobes.

causing the slightly elevated superior vermiform process to be less distinctly outlined than the inferior process is.

The cerebellum measures about three and a half inches transversely, about two and a half inches from before backward, and about two inches in depth at its thickest portion, although it thins out at its lateral borders.

FIG. 47. Cerebellum and medulla oblongata. (Hirschfeld.)

1, 1, corpus dentatum; 2, tuber annulare; 3, section of the middle peduncle; 4, 4, 4, 4, 4, laminæ forming the arbor vitæ; 5, 5, olivary body of the medulla oblongata; 6, anterior pyramid of the medulla oblongata; 7, upper extremity of the spinal cord.

The surfaces of the cerebellum are everywhere marked by deep, closely set, transverse, and somewhat curved fissures. These are often of considerable depth, the larger ones concealing many folia which do not reach the surface of the cerebellum. Some of these fissures are better marked than the rest, the most conspicuous one being the great horizontal fissure, which starts in front at the middle peduncle, and extends around the outer and posterior border of each hemisphere, being prolonged into the posterior notch, where it joins with its fellow of the opposite side. This fissure separates the cerebellum into an upper and lower portion, which correspond to the upper and lower surfaces. Each of these portions is likewise subdivided by fissures, somewhat more distinct than the rest, into small lobes. The names of these lobules can be