688 SPECIAL SENSES. 



by the crystalline lens and the anterior face of its ' suspensory ligament, and 

 at its circumference, by the tips of the ciliary processes, is known as the aque- 

 ous chamber. This contains a clear liquid called the aqueous humor. The 

 iris separates this space into two divisions, which communicate with each 

 other through the pupil ; viz., the anterior chamber, situated between the 

 anterior face of the iris and the cornea, and the posterior chamber, between 

 the posterior face of the iris and the crystalline. It is evident, from the posi- 

 tion of the iris, that the anterior chamber is much the larger ; and, indeed, 

 the posterior surface of the iris and the anterior surface of the lens are in 

 contact, except, perhaps, near their periphery or when the iris is very much 

 dilated. The liquid filling the chambers of the eye is rapidly reproduced 

 after it has been evacuated, as occurs in many surgical operations upon 

 the eye. 



The aqueous humor is colorless and transparent, faintly alkaline, of a 

 specific gravity of about 1005, and with the same index of refraction as that 

 of the cornea and the vitreous humor. It contains a small quantity of an 

 albuminoid matter, but it is not rendered turbid by heat or other agents 

 which coagulate albumen. Various inorganic salts (the chlorides, sulphates, 

 phosphates and carbonates) exist in small proportions in this liquid. It also 

 contains traces of urea and glucose. 



The anterior and posterior chambers of the eye are regarded as lymph- 

 spaces communicating with the lymphatics of the conjunctiva, cornea, iris 

 and ciliary processes. In addition a lymph-space is described as existing be- 

 tween the choroid and the sclerotic. This space is supposed to communicate 

 with a perivascular canal-system around the vasa vorticosa, and through these 

 vessels, with the space between the capsule of Tenon and the sclerotic 

 (Schwalbe). The latter is connected with lymph-channels which surround 

 the optic nerve (Key and Eetzius). 



Vitreous Humor. The vitreous humor is a clear, glassy substance, occupy- 

 ing about the posterior two-thirds of the globe. It is enveloped in a delicate, 

 structureless capsule, called the hyaloid membrane, which is about -g-^Vo" of 

 an inch '(4 /u,) in thickness. This membrane adheres rather strongly to the 

 limitary membrane of the retina. In front, at the ora serrata, the hyaloid 

 membrane is thickened and becomes continuous with the suspensory ligament 

 of the lens. 



The vitreous humor itself is gelatinous, of feeble consistence and slightly 

 alkaline in its reaction, with a specific gravity of about 1005. Upon section 

 there oozes from it a watery and slightly mucilaginous liquid. This humor 

 is not affected by heat or alcohol, but it is coagulated by certain mineral 

 salts, especially lead acetate. When thus solidified it presents regular layers, 

 like the white of an egg boiled in its shell ; but these are artificial. In the 

 embryon the vitreous humor is divided into a number of little cavities and 

 contains cells and leucocytes. It is also penetrated by a branch from the 

 central artery of the retina, which passes through its centre, to ramify upon 

 the posterior surface of the crystalline lens. This structure, however, is not 

 found in the adult, the vitreous humor being then entirely without blood- 



