. A treatise on anatomy, physiology, and hygiene : designed for colleges, academies, and families. produce contraction ofits area. The posterior layer is of a deep purple tint, and iscalled u-vea, from its resemblance in color to a ripe grape. How are this coat and the cornea united ? 897. Describe the What is the color of the external surface of the choroid coat ? Ofthe internal? How is it connected externally? How internally ? Whatdoes this membrane secrete upon its internal surface ? 899. Describe theiris. Of how many layers of fibres is the iris composed ? What is thefunction o
. A treatise on anatomy, physiology, and hygiene : designed for colleges, academies, and families. produce contraction ofits area. The posterior layer is of a deep purple tint, and iscalled u-vea, from its resemblance in color to a ripe grape. How are this coat and the cornea united ? 897. Describe the What is the color of the external surface of the choroid coat ? Ofthe internal? How is it connected externally? How internally ? Whatdoes this membrane secrete upon its internal surface ? 899. Describe theiris. Of how many layers of fibres is the iris composed ? What is thefunction of the radiating fibres r Of the circular ? ANATOMY OF THE ORGANS OF VISION. 397 900. The ciliary processes consist of a number of trian-gular folds, formed, apparently, by the plaiting of the internallayer of the choroid coat. They are about sixty in external border is continuous with the internal layer ofthe choroid coat. The central border is free, and rests againstthe circumference of the crystalline lens. These processesare covered by a layer of the pigmentum nigrum. Kg. Fig. 138. A*view of the anterior segment of a transverse section of the globe ofthe eye, seen from within. 1, The divided edge of the three coats — sclerotic, cho-roid, and retina. 2, The pupil. 3, The iris : the surface presented to view in thissection being the uvea. 4, The ciliary processes. 5, The scalloped anterior borderof the retina. 901. The retina is composed of three layers: The ex-ternal ; middle, or nervous ; and internal, or vascular. Theexternal membrane is extremely thin, and is seen as a fioccu-lent film, when the eye is suspended in water. The nervousmembrane is the expansion of the optic nerve, and forms athin, semi-transparent, bluish-white layer. The vascular 900. How are the ciliary processes formed? What does fig. 138 exhibit ?901. Of how many layers is the retina composed ? Describe the externallayer. The nervous 398 ANATOMY, PHYSIOLOGY, AND HYGIENE. memb
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