. Elements of the comparative anatomy of vertebrates. Anatomy, Comparative. 212 COMPARATIYE ANATOMY Xe Vis: Co. Fig. 169. Op -Eye or a Teleostean. campanula Halleri (Fig. 169). In the interior of this structure are nerves, vessels, and smooth muscle-fibres, and the latter possibly exert an influence on the lens, draw- ing it towards the retina. The pro- cessus falciformis is never large in Ganoids and is absent in Cyclo- stomes, Elasmobranchs, and Dip- noans : the question of accommoda- tion in these Fishes is not under- stood. Externally to the choroid proper, that is, between it and the lami
. Elements of the comparative anatomy of vertebrates. Anatomy, Comparative. 212 COMPARATIYE ANATOMY Xe Vis: Co. Fig. 169. Op -Eye or a Teleostean. campanula Halleri (Fig. 169). In the interior of this structure are nerves, vessels, and smooth muscle-fibres, and the latter possibly exert an influence on the lens, draw- ing it towards the retina. The pro- cessus falciformis is never large in Ganoids and is absent in Cyclo- stomes, Elasmobranchs, and Dip- noans : the question of accommoda- tion in these Fishes is not under- stood. Externally to the choroid proper, that is, between it and the lamina fusca, lies a silvery or greenish-gold iridescent membrane, the argentea. It extends either over the whole interior of the eye (Teleosts), or is limited to the iris (Elasmobranchs). A second layer with a metallic lustre, the tapetum lucidum, is- present internally to the iridescent portion, and within this again is the chorio-capillaris of the choroid. No tapetum appears to be present in Teleostei or Petromyzon. The so-called choroid gland, pre- sent only in Teleostei and Amia, consists of a network of blood- vessels (rete mirabile) which has the form of a cushion, lying near the entrance of the optic nerve, between the argentea and pigment epithelium of the retina : it thus has nothing to do with a " ; The sclerotic is usually extensively chondrified, and not unfre- quently becomes calcified or ossified towards its junction with the cornea. The eyeball is almost always surrounded by a gelatinous tissue, penetrated by connective-tissue fibres, and in Elasmobranchs it is usually articulated on its inner circumference witli a rod of cartilage connected distally with the lateral wall of the skull. Amphibia.—The eyes of Amphibians are proportionately smaller, and their form rounder than those of Fishes, but there are many points of close correspondence between them. This is true, for instance, as regards the more or less distinctly chondrified sclerotic, the sl
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectanatomycomparative
