. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. 672 NERVOUS SYSTEM. (NERVOUS CENTRES. THE ENCEPHALON.) is lined by the pia mater. We notice here a large interval between the arachnoid and pia mater, in which a considerable accumulation of the cerebro-spinal fluid takes place, com- municating with the anterior conflux of that fluid. In this space runs the middle artery of the brain, giving off its branches to the sides and floor of the fissure. When the convolu- tions which bound the fissure are separated, a variable number of small convolutions is found, projected fro
. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. 672 NERVOUS SYSTEM. (NERVOUS CENTRES. THE ENCEPHALON.) is lined by the pia mater. We notice here a large interval between the arachnoid and pia mater, in which a considerable accumulation of the cerebro-spinal fluid takes place, com- municating with the anterior conflux of that fluid. In this space runs the middle artery of the brain, giving off its branches to the sides and floor of the fissure. When the convolu- tions which bound the fissure are separated, a variable number of small convolutions is found, projected from its floor as an insulated lobe, which is enclosed by a bifurcation of the fissure. This lobe constitutes the island (insel) of Reil. The middle segment which lies immediately behind the Sylvian fissure, is on a plane much lower than the anterior, and corresponds on either side to the deep and hollow median fossa of the cranium. It consists of two la- teral very convex lobes, commonly known as the middle lobes of the brain, which are separated from each other by a deep depres- sion. These lobes, which are very accurately limited in front by the fissure, have no exact boundary behind, but pass off very gradually into the posterior lobes of the hemispheres, as may be seen by raising up the cerebellum. The transition from the middle to the pos- terior lobe of the hemisphere is only indicated by the different character of the inferior surface of the hemisphere, the former being convex, the latter concave. The subdivision, indeed, of the cerebral hemisphere into middle and posterior lobes is purely conventional, and I agree with Cruveilhier that it ought to be dis- carded, for it has no foundation in the anatomy Fig. Base of encephalon viewed from below. A, anterior lobe; B, middle lobe; C, posterior lobe; D, cerebellum; a, olfactory nerves; 6, optic nerves; e, third pair of nerves; d, fourth pair of ditto; e, fifth pair—portio major; e', fifth pair— portio minor ; f, si
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