THE CHOEOID COAT. 



25 



free from pigment-cells ; and lymphoid cells may occur in it here and there singly 

 or in groups (fig. 28). It is loosely united to the lamina fusca by vessels and 

 bands of connective tissue enclosing pigment-cells, and the two laminae as well as the 



Fig. 28. A SMALL PORTION OP LAMINA SUPRA-CHOROIDEA. Highly magnified. (E. A. S.) 



p, pigment-cells ; /, elastic fibres ; n, nuclei of epithelioid cells (the outlines of the cells are not 

 indicated) ; /, lymphoid cells. 



uniting structures are coated with endothelium, a lymph-space being thus formed 

 between the sclerotic and choroid. This space communicates, at the places where 

 the vessels and nerves pierce the sclerotic, with that of the capsule of Tenon 

 (Schwalbe). 



The choroid proper resembles in general structure the lamina suprachoroidea, 

 but contains in addition a very large number of blood-vessels. From a difference in 

 the fineness of these constituent vessels, it resolves itself into two strata, outer and 



^T5 



>:--&/*- "-2*^ 



jja^EL.. .TS^'-Jfes.^^-^ 



&*, 



Fig. 29. SECTION OF CHOROID. (Cadiat.) 



a, membrane of Bruch : the chorio-capillaris is just above it ; b, vascular layer ; c, vein with blood- 

 corpuscles ; d, lamina suprachoroidea. 



inner ; the former containing the larger branches, and the latter the capillary 

 ramifications. A layer of connective tissue containing many elastic fibres which 

 unites the two strata, and is nearly free from pigment, is sometimes described as a 

 third or intermediate part. 



Tapetum. This intermediate layer is markedly fibrous in some mammals, and shines 

 through the layer of choroid and retina in front of it, causing the appearance known as the 

 tapetum. In other mammals and in fish the appearance of a tapetum is produced or 



