406 JAMES EOLLIN SLONAKER 



nective tissue or fibrous layer of the sclera. It is made up o^* 

 about forty layers or lamellae of delicate parallel fibers which 

 form a transparent whole, either free from nuclei or with nuclei 

 which are no longer conspicuous. The thickness of this layer 

 in the center of the cornea is .054 mm. It gradually increases 

 in thickness toward the margins- of the cornea, where it unites 

 with the sclera, it loses its transparency and becomes opaque 

 like that structure. 



The inner endothelial layer consists of a single layer of cells 

 .003 mm. thick. The substantia propria lying immediately 

 adjacent to these cells is slightly more compact than the rest of 

 the middle layer. This may be compared with a similar layer 

 described in the eye of man as a portion of the membrane . of 

 Descemet. At the circumference of the cornea the fibers and 

 the endothelial cells break up into bundles which bend around 

 to join the base of the iris and the ciliary bodies. These cor- 

 respond to the ligamentum pectinatum, and the open spaces 

 between the bundles to the spaces of Fontana of the eye of man. 



A study of the embryonic development of the sparrow eye 

 shows that the endothelial cells lining the posterior surface of 

 the cornea are derived from the vascular or chorioid coat and 

 have been separated from this layer by the formation of the 

 aqueous chamber. The ligamentum pectinatum constitutes all 

 that is left of this embryonic connection. 



The total thickness of the cornea at its center is .071 mm. 



THE CHORIOID COAT 



The chorioid coat forms the mid lie layer of the optic capsule. 

 It is the vascular coat and functions mainly in the nutrition of 

 the other layers. It consists of two principal parts: 1, The 

 chorioid proper; 2, the derived and allied structures, such as the 

 ciliary processes, the iris, the muscles of accommodation, and 

 the pecten. 



The chorioid proper is composed largely of blood-vessels and 

 lymph spaces connected by a delicate connective tissue contain- 

 ing numerous large branching pigment cells. Beiijg abundantly 



