STRUCTURE OF THE RETINA 



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cervical sympathetic and superior cervical ganglion, and the ophthalmic branch 

 of the fifth cranial nerve. 



Structure of the Retina. The retina occupies the deeper half of the 

 cup of the eyeball. It extends forward as far as the ora serrata, where its 

 complex structure changes the form to a simple epithelial layer, which lines 

 the anterior portion of the eyeball and the ciliary processes. In the center 

 of the retina is a round yellowish spot having a minute depression in its center, 

 called the yellow spot of Sommering. The depression in its center is the 



anterior ciliary arteries and 



greater arterial circle 

 angle of the iris 



meridional fibres 



ciliary muscle 



llmbus of cornea 



anterior chamber 



pithelium 



anterior limiting! 

 membrane I 



mlar spaces 



posterior chamber 

 epithelium of lei 



capsule of lens 



posterior limiting membrane 



stroma of iris 

 posterior surface of iris 

 sphincter of pupil 



FIG. 44S- Meridional Section of a Portion of the Anterior Part of the Eyeball. (Toldt.) 



fovea centralis. About 2.5 mm. to the inner side of the yellow spot is the 

 point at which the optic nerve enters and spreads out its fibers into the retina. 

 The optic nerve arises from the base of the brain and passes forward 

 toward the orbit, being covered by the membranes which cover the brain. 

 The fibers of the optic nerve are exceedingly fine, and are surrounded by the 

 myelin sheath, but do not possess the ordinary external nerve sheath. As 

 they pass into the retina they lose their myelin sheaths and proceed as axis- 

 cylinders (the cells of origin of these fibers are in the retina). Neuroglia 

 supports the nerve fibers in the optic nerve trunk. In the center of the nerve 

 is a small artery, the arteria centralis retina. The number of fibers in the 



