284 HUMAN PHYSIOLOGY 



The blood leaves the eye : 



(1) By the central vein of the retina (from the retina). 



(2) By the vorticose veins (from the choroid). 



The aqueous humor may be regarded as lymph which, in 

 the posterior chamber of the eye, is secreted by the ciliary 

 processes and the posterior surface of the iris. The dis- 

 charge of the aqueous humor takes place in the anterior 

 chamber in the angle between the sclerotic and the iris. 

 The lymph is here absorbed into a venous vessel, the canal 

 of Schlemm (s, Fig. 30), There are no special lymph ves- 

 sels in the eye. 



The vitreous Jiumor is a jelly-like tissue, consisting of an 

 alkaline fluid inclosed in a delicate membrane. This mem- 

 brane is composed of collagen ; the fluid contains 1 . 3$ solids, 

 including traces of albumin and globulin, also a proteid sub- 

 stance called mucoid, and finally 9$ salts. The lens is com- 

 posed of fibres which may be regarded as cells ; these contain 

 about 36$ solids, chiefly a globulin-like proteid (35$). 



