the centre of vision. Two white bands on each side connect them with optic thalamus and optic tracts, those passing from the anterior pair, or nates, to thalamus are the brachia anteriora, those running from the posterior pair, the testes, to the thalamus are the brachia posteriora; passing from the testes to the cerebellum on each side is the processus e cerebello ad testes or inferior cerebellar peduncle. What is the valve of Vieussens ? A thin lamina of nerve tissue, stretching from the vermiform process of cerebellum from one processus e cerebello ad testes to the other, forming the roof of the iter e tertio, etc.: a little ridge descending upon the upper part from the corpora quadrigemina is the frænulum, and on either side are the transverse fibres connecting the fourth nerves. What is the pineal gland? A reddish conical body lying beneath the nates, connected by its base by two peduncles to the anterior crura of fornix: the gland has a small cavity-said by some to open into that of the third ventricle-containing a viscid fluid and a sandy substance, the acervulus cerebri, composed of calcium carbonate and phosphate, magnesium and ammonium phosphate, with some animal matter. Describe the medulla oblongata. It is the upper enlarged part of spinal cord, extending from upper border of atlas to lower border of pons Varolii; its posterior surface forms the floor of the fourth ventricle, its anterior rests on the basilar groove of the occiput. It contains the vaso-motor, cardiac, and respiratory centres, also those of deglutition, mastication, etc. Divided into lateral halves by the anterior (d, Fig. 80) and, Posterior median fissures, it presents on each side of anterior fissure, The anterior pyramid (p, a, Fig. 80) formed by antero-lateral columns of the cord, these latter fibres decussating above d (crossing from one pyramid to that of the other at the lower part; behind the pyramid is the olivary bodyo containing in its interior a capsule of gray matter, the corpus dentatum; behind the olivary body is, The lateral tract continuous with lateral tract of the cord; back of this is the restiform body, continuous with posterior columns of cord below, above passing into corresponding hemisphere of ceiebellum forming its inferior peduncle; running along the posterior median fissure on either side are the Posterior pyramids continuous with posterior median. columns of cord; diverging above, they form the lateral boundaries of the calamus scriptorius. Describe the cerebellum. It is that portion of the encephalon contained in the inferior occipital fossa composed of lamina covered with gray matter; on the upper surface the two hemispheres are seen connected by a median elevated lobe, the superior vermiform process, while they are separated in front and behind by notches respectively called the incisuræ cerebelli anterior and posterior; the superior vermiform process consists of a lobulus centralis in incisura anterior, the monti culus cerebelli the central projecting portion, and the commissura simplex, near the incisura posterior. Describe the under surface of the cerebellum. It is divided by a central longitudinal depression, the valley, into two hemispheres. Projecting from the bottom of the valley is the inferior vermiform process, consisting of the commissura brevis in the posterior notch, in front of the conical pyramid, more anteriorly, the uvula, lying between two rounded lobes the amygdala or tonsils, and which projects into fourth ventricle, and finally in front of uvula the nodule; attached to each side of nodule and also to flocculus, is a thin white layer which together form the posterior medullary velum. Name the lobes of the cerebellum. Below, from before backward, they are, on each side, The flocculus, or pneumogastric lobule, a prominent tuft below and behind middle peduncle. The amygdala, just described. The digastric, on outside of tonsils, partially connected with pyramid. The slender, behind former, connected with commissura brevis and back of pyramid. The inferior posterior, joining the commissura brevis in the valley. Only one fissure-the great horizontal-pertains to the cerebellum, commencing in front at pons, and passing horizontally round free margin of each hemisphere to median line; from this numerous secondary fissure proceed, marking out lobes, as two on the upper cerebellar surface on each side, viz., the anterior, or square globe, extending back to posterior edge of vermiform process, and the posterior, or semilunar, passing from preceding to great horizontal fis sure. How many peduncles has the cerebellum? Three; the transverse fibres of pons Varolii, or middle peduncle; on each side the resti form bodies of medulla oblongata, or inferior peduncles; and the processus e cerebello ad testis, forming the supe rior peduncles. Describe the arrangement of the gray matter of the cerebellum. A vertical section reveals a central stem of white matter containing a capsule of gray matter, the corpus dentatum. From the central white stem ten or twelve plates, or lamina, spring, giving origin to smaller secondary and tertiary laminæ, covered externally by a layer of gray matter, so that the cut surface presents the foliated appearance giving origin to the name arbor vitæ. The Spinal Cord. What is the spinal cord? The elongated cylindrical part of the cerebro-spinal axis contained in the vertebral canal, measuring about seventeen inches in length, extending from upper border of atlas to lower border of body of first lumbar vertebra, presenting a cervical enlargement from third cervical to first or second dorsal vertebra, and a lumbar enlargement opposite last two or three dorsal vertebræ; it terminates by a slender filament of gray substance, the filum terminale. The white matter is disposed externally, the gray internally in the form of two crescents joined by a transverse commissure, the anterior thicker extremities, forming the anterior cornua, or horns, the posterior the posterior cornua. How many membranes has the cord? Three; the dura mater, continuous with that of brain, but separated from bony walls by loose areolar tissue, containing a plexus of veins; the arachnoid, continuous with cerebral arachnoid, also having a subdural and subarachnoidean space, the latter communicating with general ventricular cavity of brain by the foramen of Magendie, an aperture in pia mater of fourth ventricle-this space contains an abundant serous secretion, the cerebro-spinal fluid; and the pia mater, sending processes down into anterior and posterior median fissures, having medianly in front a fibrous band, the linea splendens, and on each side another, the ligamentum denticulatum, whose outer border presents about twenty serrations, the apices of each attached to inner surface of dura mater, serving to support the cord. Describe the fissures. They are the anterior and posterior median, dividing cord into two lateral halves, joined medianly by a white commissure; on each side of anterior fissure is a series of foramina for the exit of anterior roots of nerves; this line of openings is called the antero-lateral fissure; two postero-lateral fissures run parallel to posterior median fissure, giving exit to posterior roots; finally, a delicate groove on each side between the postero-lateral and posterior median fissures exists, marking off the posterior pyramids. Name the columns of the cord marked off by these fissures. On each side the anterior, continuous with the anterior pyramid of medulla oblongata. The lateral, continuous with lateral tract of medulla oblongata. The posterior, continuous with restiform body of medulla oblongata. The posterior median, continuous with posterior pyramid of medulla oblongata. What is the ventricle of the cord? The foetal central canal, usually obliterated, except for a few lines below floor of fourth ventricle of brain. The Cranial Nerves. How many pairs of cranial nerves are there? Nine, according to most anatomists; twelve, according to others. Describe each of the following nerves, giving their number according to each classification. 1/ First, Olfactory 1 (Fig. 80), nerve of smell; superficial origin, by one root from middle lobe, two from anterior lobe (see p. 191); deep origin, gray nucleus in Second O Soptic FoR Optic", nerve of sight; deep origin, from optic tracts", which arise from optic thalami, corpora geniculata, and nates of corpora quadrigemina; is also attached to crus cerebri and receives fibres from tuber cinereum, lamina cinerea, and, according to some, the tænia semicircularis and gyrus fornicatus; in front of tuber cinereum lies the optic chiasm or commissure, formed of six sets of fibres, viz., a set crossing from right side of brain to left eye, a |