. Cave vertebrates of America; a study in degenerative evolution. Cave animals; Heteropygii. OPTIC LOBES OF AMBLYOPSIS. 107 (3) An optic cell layer. (4) A deep cell layer. According to Krause this layer contains in its outer part the cells which serve as terminal stations for the optic nerve, and in its inner sublayer the end stations for the fifth layer (Marklager). (5) A deep fiber layer. (6) A granular layer. (7) The ependyma and its epithelium, which lies next to the ventricle of the lobes. The optic lobes of Amblyopsis show a marked degeneration. The dorsal walls are not more than half or
. Cave vertebrates of America; a study in degenerative evolution. Cave animals; Heteropygii. OPTIC LOBES OF AMBLYOPSIS. 107 (3) An optic cell layer. (4) A deep cell layer. According to Krause this layer contains in its outer part the cells which serve as terminal stations for the optic nerve, and in its inner sublayer the end stations for the fifth layer (Marklager). (5) A deep fiber layer. (6) A granular layer. (7) The ependyma and its epithelium, which lies next to the ventricle of the lobes. The optic lobes of Amblyopsis show a marked degeneration. The dorsal walls are not more than half or two-thirds as thick as those in the normal brain. Its contour is so flattened that the ventricle is almost obliterated (16 in fig. 34 b). The torus longitudinalis, which in the normal brain is suspended in the ventricle in the median line entirely below the layers of the lobes, is between the lobes and on nearly the same level with them. The torus thus forms a commissure connecting the lobes. The band of fibers connecting them dips downward in the normal brain and crosses to the opposite side through the torus; in the degenerate lobe they cross from one side to the other in almost a straight line (15 in fig. 34 b). The shrinkage in length is shown in the fact that the hypophysis is crowded forward to the anterior level of the lobes-. ^14 Fig. 34. (a) Cross-section of Brain. Amblyopsis spelceus near Anterior part of Optic Lobes. Specimen 77 mm. long. (b) Cross-section through Middle of Optic Lobes of Amblyopsis spelceus. Specimen 77 mm. long. i, first layer of optic lobe; 2, degenerate optic fiber layer; 3, optic cell layer; 4, deep cell layer; 5, deep fiber layer; 5 a, diagonal fibers of deep fiber layer; 6, granulated layer; 7 a, optic tract region; 13, ependyma; 15, torus longitudinalis; 16, ventricle. The optic nerve of the normal brain is derived from the second and fourth layers of the lobes. The fibers of the second layer pass downward on both sides of the lobes, and the
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