. Elements of comparative anatomy. Anatomy, Comparative. VISUAL ORGANS OF MOLLUSCA. 355 at \ k—J 1-8 -<IB a kind of orbital cavity. In Nautilus tlie optic capsule is continuous with the stalk; in the Dibranchiata it is placed in the cartilaginous orbits, where it encloses the ganglionic enlai'gement of the optic nerve (Fig. 188, go), which is represented in Nautilus by a layer which extends over a larger portion of the bulb. Anteriorly, the optic capsule forms a thin investment (G), which is known as the cornea; and the refractive media of the bulb are placed behind it. This cornea is absen
. Elements of comparative anatomy. Anatomy, Comparative. VISUAL ORGANS OF MOLLUSCA. 355 at \ k—J 1-8 -<IB a kind of orbital cavity. In Nautilus tlie optic capsule is continuous with the stalk; in the Dibranchiata it is placed in the cartilaginous orbits, where it encloses the ganglionic enlai'gement of the optic nerve (Fig. 188, go), which is represented in Nautilus by a layer which extends over a larger portion of the bulb. Anteriorly, the optic capsule forms a thin investment (G), which is known as the cornea; and the refractive media of the bulb are placed behind it. This cornea is absent from the eye of Nautilus, as is the lens. In front of this cornea the optic capsule is therefore directly continuous with a mem- brane which is C connected with the integument of the optic stalk, and which has a pupil-like orifice which leads into the interior of the bulb. In the Di- branchiata this direct communi- cation between the internal cavity of the bulb and the surrounding me- dium is broken by a lens (L); as, however, in many forms (Loli gopsis, Histio- theutis, etc.), the transparent por- tion of the optic capsule is alto- gether absent or is perforated (Sepia, Loligo, Octopus), the anterior surface of the bulb enclosed in the capsule is bathed by water. This space, which communicates with the exterior, is not only continued through the optic cleft as far as the lens, but also extends more or less around the bulb. In many the integument is thrown into folds around the cornea; these folds form " eye-lids/; and are either limited in position or extend around a larger portion of the bulb, when they form a defensive organ for the eye by the possession of occlusor muscles. The base of the bulb is formed by a cartilaginous capsule (Fig. 188, 7c); around the pupil this becomes converted into the 2 a 2. Fig. 188. Horizontal section of the eye of Sepia (Diagram- matic). KK Cephalic cartilages. C Cornea. ci Ciliary body of the lens. Ri Internal layer of the ret
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Keywords: ., bookcentury1800, bookdecade1870, booksubjectanatomycomparative
