. Animal and vegetable physiology, considered with reference to natural theology. Biology; Physiology; Plant physiology; Natural theology. ^. VISION. 349 however convex, would be inconsiderable; and the chief agent for performing the requisite refraction of the rays is the crystalline lens. We, accordingly, in general, find the cornea nearly flat, and the globe of the eye approaching in shape to a hemisphere; while the lens itself is nearly sphe- rical, and of great density. The circumstances are shown in the section of the eye of the Ferch, Fig. 430.''' The flatness of the cornea leaves scarc
. Animal and vegetable physiology, considered with reference to natural theology. Biology; Physiology; Plant physiology; Natural theology. ^. VISION. 349 however convex, would be inconsiderable; and the chief agent for performing the requisite refraction of the rays is the crystalline lens. We, accordingly, in general, find the cornea nearly flat, and the globe of the eye approaching in shape to a hemisphere; while the lens itself is nearly sphe- rical, and of great density. The circumstances are shown in the section of the eye of the Ferch, Fig. 430.''' The flatness of the cornea leaves scarcely any space for aqueous humour, and but little for the motions of the iris. The surface of the eye in fishes, being continually washed by the water in which it is immersed, requires no provision 43Q of a secreted fluid for that purpose; and there are consequently neither lacrymal apparatus, nor proper eye-lids; the integu- ments supplying only a thin transparent membrane, which passes over and protects the cornea, serving the oilice of a conjunc- tiva. The eye retains its form by the support it receives from the sclerotic coat, which is of extraordinary thickness and density. In the Shay^k and the Skate the eye is sup- ported from the bottom of the orbit, by a cartilaginous pe- dicle, which enables it to turn as on a pivot, or lever. Sir David Brewster has recently made an interesting ana- lysis of the structure of the crystalline lens of the Cod, to which he was led by noticing some remarkable optical ap- pearances presented by thin layers of this substance when transmitting polarized light. He found that the hard cen- tral portion is composed of a succession of concentric, and perfectly transparent, spheroidal lamina}, the surfaces of which, though apparently smooth, have the same kind of iridescence as mother-of-pearl, and arising from the same cause; namely, the occurrence of regularly arranged lines, • In this figure, as in the others, c is tlic cornea; l, the lens; v,
Size: 1646px × 1518px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury18, booksubjectnaturaltheology, booksubjectphysiology
