THE SUSPENSORY LIGAMENT. 229 



The posterior boundary layer is a thin hyaline layer corre- 

 sponding to the vitreous layer of the choroid. 



The pigment-layer is a continuation of the retina (pars 

 iridica retinae), and consists of densely pigmented epithelium- 

 cells, fusiform anteriorly, polygonal posteriorly. 



The membrana lirnitans iridis is a delicate cuticular mem- 

 brane covering the pigment-layer posteriorly. 



The aqueous humor consists of lymph, containing a few 

 leukocytes ; it occupies the anterior chamber of the eye, which 

 is essentially a large lymph-space communicating with the 

 ocular lymphatics and is lined with endothelium, the same 

 layer which covers the posterior surface of the cornea and 

 anterior surface of the iris. 



The crystalline lens consists of a mass of epithelioid lens- 

 fibres covered by a layer of epithelium anteriorly ; the whole 

 enveloped in a capsule. 



The anterior epithelium is a single layer of low columnar 

 cells covering the anterior surface of the lens beneath the 

 capsule. 



The lens-fibres, composing the bulk of the lens, are long 

 curved hexagonal fibres cemented together, arranged some- 

 what concentrically and meridionally. Oval nuclei are pres- 

 ent near the middle of the fibres at the equator of the lens, 

 and in all the fibres when young. The lens-fibres are greatly 

 elongated epithelium-cells, derived from the posterior epithe- 

 lium of the embryonic lens. At the equator of the lens a 

 transition from the anterior epithelium into the posterior 

 epithelial fibres is observable. 



The capsule is an elastic cuticular membrane enveloping 

 the lens. 



The suspensory ligament (zone of Zinn, zonula ciliaris) en- 

 circles and supports the lens, being attached to the capsule of 

 the latter near the equator. It is a fibrous structure, radially 

 plicated ; it is connected posteriorly with the hyaloid mem- 

 brane of the vitreous body, and with the ciliary body and 

 processes, so that contraction of the ciliary muscle relaxes it 

 and permits the elastic lens to increase in convexity and re- 

 fractive pow r er. At its union with the lens it splits into two 

 layers, anterior and posterior, with a lymph -space between 

 thenx, called the canal of Petit. 



