THE CHOROID. 415 



is continuous with the sclerotic, and is formed of fifty or 

 sixty loosely-woven layers of fibrous tissue held together 

 by a cement substance. In the meshes of these lamellae 

 are the corneal spaces, containing connective-tissue cells. 

 The posterior elastic lamina is a brittle, homogeneous 

 structure about T7 V^ mcn ^ n thickness. When fractured, 

 its tendency is to roll inward. The internal epithelial 

 layer consists of a single layer of flat cells lining the 

 posterior surface of the cornea. 



THE CHOROID. 



The choroid is the vascular tunic of the eye ; it is 

 attached to the sclerotic by delicate connective tissue, 

 the lamina fusca, and invests the posterior five-sixths 

 of the eyeball ; it terminates abruptly at the ciliary liga- 

 ment, and divides, forming the iris and ciliary processes. 

 The choroid is formed of an outer, coarse, vascular, and 

 an inner capillary layer, containing scattered pigment 

 cells. Posteriorly it is pierced by the optic nerve. The 

 ciliary ligament is a band of involuntary muscular fibres, 

 about three millimetres in width, thicker in front than 

 behind, and attached to the anterior portion of the cho- 

 roid, to the anterior margin of the sclerotic, and inter- 

 nally to the iris and ciliary processes. The iris is a circu- 

 lar, vertical, muscular, perforated curtain, suspended 

 between the cornea and crystalline lens ; it presents an 

 anterior and posterior surface, and the perforation or 

 pupil. The surfaces are covered by flat cells, continuous 

 with the endothelial lining of the cornea. A few fibres 

 pass at intervals from the posterior elastic lamina of the 

 cornea; they constitute the pectiniform ligament of the 

 iris. The spaces between these fibres aie the spaces of 

 Fontana. These communicate with a circular sinus. 

 the canal of Schlemm, which runs near the junction 



