MINUTE STRUCTURE OF CEREBELLUM. THE CEREBRUM. 529 



they form a thin light-coloured lamina, intermediate between two darker strata of 

 grey matter which contain the nerve-cells ; one of these grey strata being the deepest 

 and next the white matter of the cerebellum, while the other, which is the darker 

 coloured of the two, is in contact with the pia mater. 4. Fibres. Tubular nerve- 

 fibres pass from the white into the grey matter, and extend through it nearly as far 

 as the surface. The mode of their termination, which is difficult to trace, has been 

 investigated by various anatomists. According to Valentin, they form loops and 

 return upon their course, but this statement has not been confirmed by other 

 observers. 



Gerlach has recently described a very remarkable arrangement of the fibres of the 

 cerebellum. According to him, these fibres, on approaching the grey matter, split 

 up into extremely fine divisions, which form a network, while the granules, which he 

 considers as small cells with ramifying processes, are placed at the angles of the 

 meshes, and branching processes of the large nerve-cells also terminate in the network. 

 According to Kb'lliker, networks of tubular fibres exist within the grey matter and 

 communicate with the nerve-cells, while the granules belong to the reticulum of 

 connective tissue. Luys, like Gerlach, describes lateral processes as being given oft' 

 by the nerve-fibres to connect them with the granules, at the same time that they 

 terminate likewise directly, although much attenuated, in the large nerve-cells. 

 (Gerlach, "Microscopische Studien," pi. I., fig. 3; copied in Yirchow's "Cellular 

 Pathology/' by Chance, p. 269.) 



THE CEREBRUM. 



The cerebrum, or brain proper, constitutes the highest and much the 

 largest portion of the encephalon. It consists of the following parts, viz., 

 the peduncular masses of the crura cerebri and processus a cerebello ad 

 cerebrum ; the series of eminences or cerebral centres or ganglia concealed 

 from view, named corpora quadrigemiua, optic thalami and corpora striata ; 

 the cerebral hemispheres, which are by far the most bulky part of the cere- 

 brum and of the whole encephalon, and form nearly the whole superficial 

 part ; various commissural structures including the corpus callosum and 

 fornix; and lastly some smaller structures, viz., the pineal and the pituitary 

 bodies, and the olfactory bulbs. 



EXTERIOR OF THE CEREBRUM. 



The cerebral hemispheres together form an ovoid mass, flattened on its 

 under side, and placed in the cranium with its smaller end forwards, its 

 greatest width being opposite to the parietal eminences. They are separated 

 in the greater part of their extent by the great longitudinal fissure. 



Each cerebral hemisphere has an outer or convex surface, which is in 

 contact with the vault of the cranium ; an inner or flat surface, of a crescent 

 shape, which forms one side of the longitudinal fissure ; and an irregular 

 under surface, which rests on the base of the skull, and on the tentorium 

 cerebelli. 



Three lobes, or large divisions, projecting in three different directions, have 

 usually been distinguished in each hemisphere, under the names of anterior, 

 middle, and posterior lobes. The division between the anterior and middle 

 lobes is very clearly denned below and on the sides by a deep cleft, named 

 the Sylvian fissure. There is no similar demarcation between the middle 

 and posterior lobes ; but anatomists have generally considered as the pos- 

 terior lobe that part of the hemisphere which lies over the cerebellum. 

 The under surface of the anterior lobe is triangular and excavated to adapt 

 it to the roof of the orbit on which it rests. The middle lobe is rounded 



