. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. NEKVOUS CENTRES. (HUMAN ANATOMY. THE MENINGES.) (537 culs-de-sac at the orifices through which the nerves escape. Fig. Traitsverse section of the same on a level with the fifth cervical nerves. (After Arnold.) The same parts arc displayed as in the last figure, and the reflection of the arachnoid at the exit of the nerves is seen. af, anterior fissure ; n, n, spinal nerves. In the interval between each pair of nerves, we find a triangular process of fibrous mem- brane which is inserted by its apex into the dura mat
. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. NEKVOUS CENTRES. (HUMAN ANATOMY. THE MENINGES.) (537 culs-de-sac at the orifices through which the nerves escape. Fig. Traitsverse section of the same on a level with the fifth cervical nerves. (After Arnold.) The same parts arc displayed as in the last figure, and the reflection of the arachnoid at the exit of the nerves is seen. af, anterior fissure ; n, n, spinal nerves. In the interval between each pair of nerves, we find a triangular process of fibrous mem- brane which is inserted by its apex into the dura mater. This process lies in the sub- arachnoid cavity and adheres by its base to the pia mater. It seems to pierce both layers of the arachnoid, or to pin them down, as it were, to the dura mater. At the foramen magnum the spinal arach- noid may be seen to be continuous with that of the brain, and here its visceral layer invests the medulla oblongata loosely. Interiorly we trace the membrane down quite to the lowest extremity of the dura mater, and in this region the visceral layer is particularly loose and free, as it lies over the cauda equina. When the dura mater is carefully slit up along either the anterior or the posterior surface, the arachnoid sac is laid open. It does not always happen that the parietal layer separates very readily from the visceral: frequently the two layers adhere firmly at j-everal minute points, yet this adhesion is effected without any connecting membrane, and appears to arise from the two layers becoming dried at several corres- ponding points, and thus being, as it were, glued together. We may frequently observe this in specimens that have been some time kept in spirits. This point is deserving of notice, as these adhesions might be (and indeed they have been) noted as of a morbid nature. The visceral layer of the spinal arachnoid is connected to the pia mater by means of a num- ber of loivj; filaments of fibrous tissue which in- terlace slightly,
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