740 



SIGHT. 



FIG. 158. 



rated by minute openings for the passage of the nerve-filaments. One of 

 these openings, which is relatively large, gives passage to the arteria centralis 

 retinae. Surrounding this point of entrance of the optic nerve are many 

 small openings for the passage of the ciliary nerves and vessels. The in- 

 ternal surface of the sclera contains some 

 pigment granules. It is separated from 

 the choroid coat by a delicate flocculent 

 cellular tissue, called the lamina fusca. 



The choroid coat is a vascular membrane 

 containing some pigment granules. The 

 external portion is composed principally 

 of bloodvessels and nerves. Between the 

 vessels are found numerous stellate pig- 

 ment-cells, which form a fibrous network. 

 The internal surface, where it adjoins the 

 pigment layer of the retina, also contains 

 pigment-cells. Posteriorly it is pierced 

 by the optic nerve ; anteriorily it is con- 

 tinuous with the ciliary processes, and is 

 separated from the sclerotic coat by the 

 ciliary muscle. 



The ciliary processes are arranged in the 

 form of a ring. They consist of about sixty 

 to eighty somewhat conical-shaped bodies, 

 situated with their bases internally. (Fig. 

 158.) They are placed posterior to the 

 iris, and are attached by their thickened 

 or internal extremities to the suspensory ligament of the lens. 



The ciliary muscle arises from the point of junction of the sclerotic coat 

 and the cornea. It consists of two portions a radiating or meridional and 

 a circular layer. The radiating fasciculi are situated externally and have a 

 meridional direction. (Fig. 159.) From this layer numerous fasciculi inter- 



inner View of the Front of the 

 Choroid Coat with its Ciliary Processes, 

 and the Back of the Iris, a, anterior 

 piece of the choroid coat ; b, ciliary pro- 

 cesses ; c, iris ; d, sphincter of the pupil ; 

 e, bundles of fibres of the dilator of the 

 pupil. 



FIG. 159. 



Section of the Ciliary Region of the Eye in Man. a, meridional muscular fasciculi of the 

 musculus ciliaris ; b, deeper-seated radiating fasciculi ; c, c. c, annular plexus ; d, annular muscle 

 of Muller : /, muscular lamina on the posterior surface of the iris ; g, muscular plexus at the 

 ciliary border of the iris ; e, annular tendon of the musculus ciliaris; h, ligamentum pectinatum. 



lace between the fasciculi of the circular layer, which occupies an internal 

 position to the radiating layer. The ciliary muscle is inserted into the 

 external surface of the anterior portion of the choroid coat, the fibres extend- 

 ing somewhat posterior to the anterior margin of the retina. This muscle is 

 a very important factor in the mechanism of accommodation. 



