H56 



HUMAN ANATOMY. 



FIG. 1211. 



Portion of injected choriocapillaris layer of 

 human choroid. X 13- 



Structure of the Choroid. The choroid consists of four layers, which from 

 without inward, are : (i) the lamina suprachorioidca, (2) the choroid proper, which 

 contains the larger vessels, (3) the choriocapillaris, or layer of fine capillaries, and 

 (4) the membrana vitrea. 



The lamina suprachorioidea forms the outer boundary of the choroid and 

 connects it with the sclera. It is composed of interlacing bundles of fibrous connec- 

 tive tissue, which are strengthened by a rich net- 

 work of elastic fibres. The cellular elements 

 consist of (a) flattened endothelial plates, which 

 line the lymph-clefts and cover the connective 

 tissue trabeculae connecting the choroid and the 

 sclera by traversing the suprachoroidal lymph- 

 space ; and (^) large, irregularly branched con- 

 nective tissue cells, the chromatophorcs, which 

 are conspicuous on account of their deeply 

 pigmented protoplasm. The lamellae of the 

 suprachoroid continue, without definite boun- 

 dary, into the subjacent choroidal stroma. 



The choroid proper, as the choroidal 

 stroma is called, has the same general structure 

 as the suprachoroidal layer, but the connective 

 tissue elements are denser and support a large 

 number of blood-vessels, between which are 

 placed the stellate chromatophores. The largest 

 vessels occupy the outer part of the coat, and 

 are chiefly venous. They are surrounded with 

 perivascular lymph-sheaths, and converge in peculiar whorls to form four or five 

 large trunks, the vena vorticostz, which pierce the sclera in the equatorial region and, 

 running obliquely backward, drain not only the choroid, but partly also the ciliary 

 body and iris. The arteries are derived from the short ciliary vessels, which pass 

 through the sclera near the optic nerve. 

 They lie internal to the veins and their 

 walls contain longitudinally disposed muscu- 

 lar fibres in addition to the customary cir- 

 cular ones. 



The choriocapillaris, or membrane of 

 Ruysch, is composed of the fine capillaries 

 of the choroidal vessels, which form an 

 extremely fine mesh-work embedded within 

 a homogeneous, nonpigmented matrix. 

 Between the choriocapillaris and the layer of 

 larger vessels is a narrow boundary zone of 

 closely woven fibro-elastic strands, which is 

 nearly free from pigment. In some animals 

 this layer possesses a peculiar metallic reflex 

 and is known as the tapctnm fibrosum ; in 

 carnivora its iridescent appearance is clue to 

 the presence of cells containing minute crys- 

 tals (tapelum ce//n/osi/i\ 



The membrana vitrea, or membrane 

 of Bruch, the innermost layer of the choroid, 

 measures only .002 mm. in thickness. It 

 separates the choriocapillaris from the 

 retina and is composed of two strata, an 

 Miner homogeneous one, probably an exu- 

 dation product of the retinal pigment cells, and an outer highly elastic portion. 

 The lymphatics of the choroid are represented (i) by vessels which begin in tin- 

 lymph-spaces between lar^e blood-vessels, and are in communication with the spaces 

 between the suprachoroidal lamellae, and (2) by the perivascular lymph-spaces of 



FlG. 1212. 



Sclera 



Iris 



Cornea 



Ciliary ring 

 Ora serrata 



Anterior part of sasittally sectiomM . 

 showing iris, ciliary processes and ring and ora 

 serrata. X 3. 



