Diseases of the nervous system / edited by Archibald Church.

Date:
1908
Catalogue details

Licence: In copyright

Credit: Diseases of the nervous system / edited by Archibald Church. Source: Wellcome Collection.

    52/1256 (page 24)
    sections up to the lemniscus decussation, which then becomes visible medially as an open, peculiarly serrated, arc-like body behind the pyramids. In the upper portions of the medulla, dorsally and laterally, we note the large corpus restiforme which in its downward path rapidly decreases in size and finally disappears. On the other hand, the lower half of the medulla oblongata after the fourth ventricle has closed to the narrow central canal, dorsally of the latter, the nuclei of the spinal posterior columns, the nucleus gracilis and the nucleus cuneatus appear, while from the pons up to the upper spinal cord the so-called ascending root of the trigeminal nerve (which in reality degenerates downward in combination with the substantia gelatinosa which passes into the posterior horn of the spinal cord) becomes prominent. The nuclei of the cranial nerves from the ninth to the twelfth are situated in the dorsal portion of the medulla, some immediately upon the floor of the fourth ventricle; they are insusceptible to macroscopic investigation. Medially behind the pyramids is the lemniscus layer which, immediately above the well known pyramidal decussation, forms the lemniscus decussation. Before passing to the study of the spinal cord which begins at the height of the pyramidal decussation, we will briefly review the structures at the base of the brain, arranged in an antero-posterior direction. Their relations are of practical importance inasmuch as we know there are a number of basal processes, tumors, syphilitic exudates, etc., in which an exact, local diagnosis necessitates a knowledge of the sequence of these individual parts, particularly the order in which the cranial nerves are affected. Äfost ante- riorly at the base of the brain and below the frontal lobes are the olfactory bulbs, which narrow posteriorly toward the olfactory tract. Behind them is the substantia perforata anterior, above which thin white strands, the roots of the olfactory nerve, pass into the medulla of the hemispheres. Posteriorly to these is the optic chiasm from which the optic tracts run posteriorly and outwardly, surrounding the cerebral peduncles, and extend- ing to the thalamus opticus and the corpora quadrigemina. Behind the optic chiasm we find the floor of the third ventricle, the tuber cinereum with the infundibulum, at the extremity of which is the hypophysis. This latter struc- ture has in the last few years attracted great attention because it has fre- quently been found to be enlarged in acromegalia, and the pressure upon the chiasm has produced bitemporal hemianopsia. In how far these enlarge- ments of the hypophysis are the cause of acromegalia has not yet been deter- mined. Behind the hypophysis are the two corpora mammillaria, also a gray substance, the substantia perforata posterior, lying upon the floor of the subthalamic region between the two cerebral peduncles. At either side of this structure the cerebral peduncles pass posteriorly and medially to the pons. The oculomotor nerve appears in front close to the origin of the great trans- verse fibers of the pons and on each side of the internal border of the pedun- cles, while somewhat further on, and posteriorly between the lateral posterior border of the peduncles and the pons, the trochlear nerve arises. The fifth nerve with its narrow motor and broad sensory divisions emerges from the lateral posterior portion of the pons. While, up to this point, the cranial nerves are isolated at the base of the brain, when the pons enters the medulla and the cerebellum begins, the origins of the cerebral nerves are close together, so that, for instance, tumors which here implicate the bones of the posterior