782 SPECIAL SENSES. 



talline lens and the anterior face of its suspensory ligament, and, at its circumference, by 

 the tips of the ciliary processes, is known as the aqueous 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 be- 

 tween 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 position 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 pe- 

 riphery or when the iris is very much dilated. The liquid filling the chambers of the eye 

 is said to be secreted by the blood-vessels of the ciliary processes ; at all events, it is rap- 

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

 the eye. 



There is very little to be said concerning the properties and composition of the aque- 

 ous humor. It is perfectly colorless and transparent, faintly alkaline, of a specific gravity 

 of about 1005, and possesses the same index of refraction as the cornea and the vitreous 

 humor. As we should infer from its low specific gravity, the aqueous humor is composed 

 chiefly of water. It contains a small quantity of an albuminoid matter, but it is not ren- 

 dered turbid by heat or other agents which coagulate albumen. Various inorganic salts 

 (the chlorides, sulphates, phosphates, and carbonates) exist in this liquid, in small propor- 

 tion. It contains also traces of urea and glucose. 



Vitreous Humor. The vitreous humor is a clear, glassy substance, occupying about 

 the posterior two-thirds of the globe. It is enveloped in an exceedingly delicate, struct- 

 ureless capsule, called the hyaloid membrane, which is about ^Vfr f an inch m thick- 

 ness. This membrane adheres pretty strongly to the limitary membrane of the retina. 

 In front, at the ora serrata, as we have already seen, the hyaloid membrane is thickened 

 and becomes continuous with the suspensory ligament of the lens. 



The vitreous humor itself is gelatinous, of feeble consistence, slightly alkaline in its 

 reaction, with a specific gravity of about 1005. Upon section, there oozes from it a 

 watery fluid of a slightly mucilaginous consistence. This humor is not affected by heat or 

 alcohol, but it is coagulated by certain mineral salts, more especially the acetate of lead. 

 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 numer- 

 ous 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 on the poste- 

 rior surface of the crystalline lens. This structure, however, is not found in the adult, 

 the vitreous humor being then entirely without blood-vessels. 



There is still considerable difference of opinion with regard to the structure of the 

 vitreous humor in the adult, some anatomists believing that it is perfectly homogeneous 

 and that the so-called laminae are produced only by the action of reagents, while others 

 state that it is divided into compartments, by processes penetrating from and connected 

 with the hyaloid membrane. The weight of authority is decidedly in favor of a sub- 

 division of the humor into compartments formed by delicate membranes radiating from 

 the point of penetration of the optic nerve to the anterior boundary where the hyaloid 

 membrane is in contact with the capsule of the lens. In this way, the humor is divided 

 up, something like the half of an orange, by about one hundred and eighty membranous 

 processes of extreme delicacy, which do not interfere with its transparency. 



Summary of the Anatomy of the Globe of the Eye. 



For the intimate structure of the various coats of the eye, their dimensions, etc., the 

 reader is referred to the descriptions just given of these parts. In this summary, we 

 propose simply to show the relations of the various parts, giving at the same time a 

 brief statement of their physiological importance. This end will be attained by a full 



