ANATOMY IX A NUTSHELL. H87 



with folds prolonged from the ciliary processes and is darkly pigmented. The 

 anterior surface is colored and marked by wavy lines which converge towards 

 the free edge of the pupil. This surface is covered by a layer of epithelium 

 which is continuous with that of the membrane of Descemet. The frame work 

 of the iris is a delicate struma which consists of connective tissue containing 

 blood vessels, nerves, pigment cells, and muscular fibers (involuntary). The 

 first, sphincter fillers which form a circular narrow band pass to the pupil and 

 receive the third nerve. This band is about one-thirtieth of an inch in thick- 

 ness. The second, dilator, which are radiating, commence at the outer margin 

 of the iris, converging towards its center to join the circular one near the pupil. 

 Some say these are elastic and not muscular. It receives the sympathetic 

 nerve. The blood supply is from the Long and anterior ciliary and the vessels 

 of the ciliary processes. Nerve supply from the ciliary branches of the lenticu- 

 lar ganglion and long ciliary branches of the nasal nerve which is a branch of the 

 ophthalmic division of the fifth. The nerves form a plexus around the mar«in. 

 The membrana pupillaris is a delicate transparent vascular membrane which 

 closes the pupil in the fetus. It disappears about the seventh month. 



The retina ends behind the ciliary muscle in an irregular margin, the ora 

 serrata. The pars ciliaris (radiating fibers of Muller covered bv pigmented 

 layers) is a thin membrane passing from the ora serratus to the iris. The 

 macula lutea is the most perfect point of vision. It is situated at the center of 

 its inner surface behind. It has a depression called the fovea centralis. The 

 poms opticus of the optic nerve is pierced by the arteria centralis retinae and is 

 one-tenth of an inch internal to the macula lutea. Mutter's fibers are connective 

 tissue fibers which bind the layers of the retina together. The aqueous humor 

 fills the anterior and posterior aqueous chambers which are situated between 

 the posterior surface of the cornea and the anterior surface of the iris and be- 

 tween the posterior surface of the iris and the anterior surface of the crystalline 

 lens. It is a slightly alkaline fluid. The lens is in contact anteriorly with the 

 iris: posteriorly it rests in the depression of the vitreous humor, fovea pupillaris. 

 It is surrounded by a capsule-zonule of Zinn which is derived from the hyaloid 

 membrane. The lens is about one-fourth of an inch antero-posteriorly and one- 

 half transversely. It is a transparent, solid, biconvex body composed of con- 

 centric laminae and is hardest at the center. The vitreous humor occupies about 

 four-fifths of the eye-ball resting upon the retina behind and is hollowed out in 

 front the fossa pupillaris for the lens. It is a soft, gelatinous substance and 

 surrounded by transparent hyaloid membrane. It fills the cavity of the re- 

 tina. The canal of Stilling runs through its center from the porus opticus to 

 the lens and is lined by a prolongation of the hyaloid membrane. This canal 

 is filled with fluid. In the fetus an artery runs from the arteria centralis retina' 

 to the capsule of the lens. At the pars ciliaris this membrane divides sending 

 a layer behind the capsule and one in front: the anterior one is the suspensory 

 ligament of the lens. It contains elastic fibers. The canal of Petit surrounds 

 the lens. (Plate CC). 



The lachrymal gland (Plate CCV) resembles serous salivary glands. It is situated 

 internal to the external angular process in a depression in the orbital plate of 



