. Text book of zoology. Zoology. Vertehrata. 337 A peculiar third unpaired eye, the pineal eye (parietal eye), in connection with the pineal body, has been recently described in some Lizards (, in the common Lacerta, Blind-worm, and others). It Ues in a small perfora- tion of the upper wall of the skull (in the parietal bone, or between this and the frontal), close below the skin, which is at this spot partially transparent. It consists of a vesicle formed of a simple epithelium, the upper portion forming a lens-like thickening, whilst the lower part is much pigmented (retina). In other Li
. Text book of zoology. Zoology. Vertehrata. 337 A peculiar third unpaired eye, the pineal eye (parietal eye), in connection with the pineal body, has been recently described in some Lizards (, in the common Lacerta, Blind-worm, and others). It Ues in a small perfora- tion of the upper wall of the skull (in the parietal bone, or between this and the frontal), close below the skin, which is at this spot partially transparent. It consists of a vesicle formed of a simple epithelium, the upper portion forming a lens-like thickening, whilst the lower part is much pigmented (retina). In other Lizards the same structure occurs in the same position in a more rudimentary form, as a simple vesicle, which does not resemble an eye, but is uupigmented, and without a lens. A structui'e Uke the first desci-ibed occurs also in the Cyclostomi, where, however, it is covered by the skull, which is often somewhat thin at this place, and may even, like the skin above it, be transparent. In various other Yertebrates also, facts are known which point to a. Fig. 277. Pineal eye of a Lizard; diagii-ammatio. ^ brain and npper wall of the skull, the latter cut through; B pineal eye alone, in section. F, Z, M, H cerebrum, thalamencephalon, optic lobes, cerebellum ; h skin, s roof of skull, o unpigmented portion of skin below which the pineal eye Kes, in a hole in the roof of the skull; p epiphysis, t hypophysis, 2 optic nerve. L lens, R retina, N nerve of pineal eye.—Orig. (using Spencer's figures). connection between the pineal gland and the exterior. In the Selachians the pineal gland is filiform, and its distal end lies in a hole in the dorsal wall of the skull, covered entirely by skin ; so far as is known it possesses no optic structure. In the A n u r a also, the epiphysis, which is short at first, elongates dm-ing larval life into a long thread, with a, terminal enlargement; the thread perforates the skuU-wall, and the swelling lies on the upper side of the head, directly beneath
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1896
