216 



THE ESSENTIALS OF HISTOLOGY 



5. A layer of pavement-epithelium covering the posterior surface of 

 the elastic lamina, and lining the front of the anterior chamber of the 

 eye (fig. 348, 5). At the sides it is continued over the ligamentum 

 pectinatum into a similar epithelium, covering the anterior surface 

 of the iris (fig. 253, N). 



The nerves of the cornea pass in from the periphery, losing their 

 medullary sheath as they enter the corneal substance. They form 

 a primary plexus in the substantia propria, a secondary or sub-epit- 

 helial plexus immediately under the epithelium which covers the 

 anterior surface, and a terminal plexus of fine fibrils which pass from 

 the sub-epithelial plexus in pencil-like tufts and become lost between 

 the epithelium-cells (see figs. 105, 106, Lesson XIX.) There are no 

 blood-vessels or lymphatics in the cornea, although they come close 

 up to its margin. 



The choroid or vascular coat of the eye is of a black colour in many 

 animals, but in the human eye is dark brown. It is composed of connec- 

 tive tissue, the cells of which are large and filled with pigment (fig. 251), 

 and it contains in its inner part a close network of blood-vessels, and 



cl.... 



FIG. 250. SECTION OF CHOROID. (Cacliat.) 



a, membrane of Bruch : the chorio-capillaris is just above it ; 6, vascular layer ; c, vessels 

 with blood-corpuscles ; d, lamina suprachoroidea. 



in its anterior part the involuntary muscular fibres of the ciliary 

 muscle, which pass backwards from their origin at the junction of the 

 cornea and sclerotic, to be inserted into the choroid. The choroid is 

 separable into the following layers, enumerated from without in 

 (fig. 250) : 



1. The lamina suprachoroidea (fig. 250, d). This is a thin mem- 

 brane composed of homogeneous connective tissue pervaded by a net- 

 work of fine elastic fibres, and containing many large branched 

 pigment-cells and lymph-corpuscles (fig. 251). It is covered super- 

 ficially by a delicate lymphatic epithelium, and is separated from the 

 lamina fusca by a cleft -like lymphatic space which is bridged across 

 here and there by the passage of vessels and nerves, and by bands of 

 connective tissue. 



2. The vascular layer of the choroid (fig. 250, b), which resembles 



