. Elements of the comparative anatomy of vertebrates. Anatomy, Comparative; Vertebrates -- Anatomy. EYE. 185 lens, iris, and of a differentiated sclerotic and cornea. Moreover, the eye of Myxinoids and of Ammoccetes lies beneath the skin and sub-dermal connective-tissue. In Petromyzon the skin covering the eye becomes thinned out, and thus the animal, which was blind in the larval state, can see on reaching the adult condition : at the same time the eyeball increases in size, and becomes more highly organised. The eyes of all the true Fishes are, with few exceptions ( Siluroids and Eels),
. Elements of the comparative anatomy of vertebrates. Anatomy, Comparative; Vertebrates -- Anatomy. EYE. 185 lens, iris, and of a differentiated sclerotic and cornea. Moreover, the eye of Myxinoids and of Ammoccetes lies beneath the skin and sub-dermal connective-tissue. In Petromyzon the skin covering the eye becomes thinned out, and thus the animal, which was blind in the larval state, can see on reaching the adult condition : at the same time the eyeball increases in size, and becomes more highly organised. The eyes of all the true Fishes are, with few exceptions ( Siluroids and Eels), of considerable size. They have but little power of movement, and as the cornea is very fiat, and the lens lies almost directly against it, the eyeball always possesses a hemispherical or ellipsoidal form, and the anterior chamber is very small. In other points, the eye is formed on the same plan as that described in the introductory portion of this chapter, but a few other details concerning it must now be considered. FIG. 153.—EYE OF A TELEOSTEAN* Op, optic nerve ; OS, sheath of optic nerve ; Rt, retina ; PE, pigment epithelium ; Tp, tapetum ; Lv, lamina vasculosa ; Ag, argentea ; Ls, lamina suprachoroidea; Se, sclerotic, enclosing cartilage or bone (t) ; Co, cornea ; Ir, iris ; Lc, ciliary ligament; VK, anterior chamber ; L, lens ; Cr, vitreous humour ; Pr, processus falciformis, and Cp, campanula Halleri, here shown as if continuous with one another. The lens of Fishes, as in all aquatic animals, is globular, and possesses therefore a high refractive index. It fills up the greater part of the eyeball, so that not much space is left for the vitreous humour. It forms an exception to that of other Vertebrates in the fact that, in the condition of rest, it is accommodated for seeing near objects. In place of a ciliary muscle, there is only a fibrous ciliary ligament. In the eye of Teleostei, a fold, the processus falciformis, arises from the choroid and extends into the
Size: 1534px × 1628px
Photo credit: © Paul Fearn / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1880, bookpublisherlondonnewyorkmacmi
