one twelve-hundredth of an inch to one fifteen-hundredth, and are more widely separated from each other in consequence of the multitude of fibres which pass everywhere between them. Indeed, they appear to be enclosed in a network of fibres and blood-vessels. They all have several processes passing in different directions from those points which are more or less angular, together with a kind of fringe-work extending along the whole border of each cell, and more especially at the points where the nerve-fibres appear to enter or leave them. The larger nerve-fibres appear to connect with the cells at both the lower and upper points, and from the lower pass to the upper spaces where they interlace with each other, and then again pass downward. They have nuclei which are also pyramidal in form, and also nucleoli which are surrounded with layers of protoplasmic material, which is more dense than that lying near the surface of the cell. These nucleoli are "also divisible into secondary filaments" (Luys), and for aught we know now to the contrary, may be found to have a most complicated structure. In the fourth layer there appears to be an almost total absence of these pyramidal cells, and in their place there is observed a large quantity of elements irregularly shaped, which is termed the "granular formation." These elements are larger in the upper portion of the layer and are grouped irregularly into clusters. Near the lower portion of the layer they become smaller and often isolated. Below this is the fifth layer, which is not very definitely bounded, but has a considerable number of cells, some of which, especially those in the upper portion of the layer, are pyramidal in form, while those in the lower portion and near the medullary substance of the brain are long and spindle-shaped. (Meynert.) They also send out processes or fibres toward the granular elements of the fourth layer. In our progress downward we next come to the medullary substance, which contains more or less of the spindleshaped cylinders, with fibres or bundles of them extending. in the same general direction as those of the layers already described. There exist also, associated or intermingled with these fibres, "branching cells," in varying numbers according to locality. Below this, though there exists no sharply defined line of division, is the white substance of the brain, which is filled with granular matter and nerve-fibres, and furnishes a cushion, as also a support, for the innumerable medullated nerve-fibres which pass through it from the cortex to the periphery. About the basal centre of the brain we find another aggregation of grey matter, though arranged in a very different manner. In a general way it may be said to be made up of several aggregations of ganglia, the larger and more important of which appear to be the optic thalami, the corpora striata, the corpora quadrigemina, and the pineal gland. The optic thalami are situated in the rear of the striate bodies, and directly above where the spinal cord enters into and becomes part of the brain. They are broader behind than on the anterior end, and have a form somewhat like the shape of a wedge. The surface of a section made across the body of the ganglia would present three angles more or less distinctly acute. They are composed largely of grey matter, arranged in layers, which is made up of nerve-cells, medullated fibres, and blood-vessels. These cells are grouped together in different portions of the thalamus, and appear to form centres around which the medullated fibres gather, and are radiated to the several portions of the cortex-anterior, posterior, and lateral. The nerve-fibres reaching the ganglia from different directions appear to cross from side to side and end to end, and form more or less distinct planes extending across the thalamic body. Luys claims that they are each composed of or contain four small ganglia. These several ganglia would, therefore, become a sort of terminal centre or pivot, around which revolve all the attractions and reflections of the nerve-fibres, which arrive here from all portions of the body, one of which is found to be connected directly with the olfactory nerve, and therefore receives all impressions made upon it; another with the optic nerve, and therefore receives and transmits all impressions produced on it. The third is intimately connected with the nerves of general sensation, which reach it through the spinal cord, while the fourth receives the impressions communicated by the auditory nerve. In this way it appears that there exist. SECTION THROUGH THE 'TWEEN-BRAIN BENEATH THE UPPER SURFACE OF THE OPTIC THALAMUS AND THE NUCLEUS CAUDATUS. THE THALAMUS, THE NUCLEUS CAUDATUS AND THE IMMEDIATELY SURROUNDING PARTS ARE SHOWN. Com, commissura mollis; 13. third ventricle; Fel, columna fornicis: Spl, septum pellucidum; 17a, anterior horn of lateral ventricle; Gcc, genu corporis callosi; Pdc, pedunculus pinealis: Glp, glandula pinealis; Q, posterior corpora quadrigemina; Qa, anterior corpora quadrigemina; gh, ganglion hebenula; Nc, nucleus caudatus; Stc, stria cornea; Na, nucleus anterior; N, nucleus lateralis. separate and, in some measure, independent centres for the reception and transmission of impressions received through |