226 THE NERVOUS SYSTEM. 



Between the sclerotic and choroid coats is a layer of loose 

 fibro-elastic tissue containing irregular pigmented connective- 

 tissue cells ; the portion of this tissue applied to the sclerotic 

 is called the lamina fusca, that next to the choroid the lamina 

 suprachoroidea ; in the midst of this tissue are ample lymph- 

 spaces (subscleral or perichoroidal) lined with endothelium. 

 Externally the sclerotic rests in a sort of synovial sac, the 

 capsule of Tenon. 



The cornea is the modified transparent anterior portion of 

 the sclerotic. It consists of five layers, which are, from before 

 backward : epithelium, anterior elastic membrane, corneal 

 substance proper, posterior elastic membrane, and posterior 

 endothelium. 



The epithelial layer covering the cornea anteriorly consists 

 of a few layers of stratified squamous epithelium, and is the 

 corneal portion of the conjunctiva; the lowermost cells are 

 columnar. 



The anterior elastic lamina (or " membrane of Bowman") is 

 a thin, hyaline, apparently homogeneous layer, forming a 

 basement-membrane for the epithelium. 



The substantia cornece propria makes up the main part of 

 the cornea, and consists of transparent lamina? of white fibres 

 bound together by cement-substance. Between the lamina? 

 are numerous stellate connective-tissue cells with anastomosing 

 branches. These cells and their processes lie in spaces form- 

 ing a network of passages through which lymph can perco- 

 late for the nutrition of the cornea, which possesses no blood- 

 vessels. 



Behind the substantia propria is the posterior elastic lamina 

 (or " membrane of Descemet "), a thin, homogeneous, hyaline 

 layer like the anterior one. Upon the free posterior surface 

 of this membrane is a single layer of endothelium-cells, con- 

 tinuous with those lining the anterior surface of the iris. 



The cornea contains plexuses and terminals of nerve-fibrils. 

 At the junction of the cornea and sclerotic, in the substantia 

 propria, is a venous or lymph-passage, the canal of Schlemm, 

 encircling the cornea. 



The choroid is the thin, middle vascular tunic of the eye. 

 Anteriorly it is continuous with the ciliary body and iris. 

 The outermost layer of the choroid is the lamina supra- 





