ANATOMY OF THE EYEBALL. 65 



nea, posteriorly 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 aqueous cham- 

 ber. This contains a clear liquid, called the aqueous hu- 

 mor. 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 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 periphery 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 rapidly reproduced after it has been evacuated, 

 as occurs in many surgical operations on the eye. 



There is very little to be said concerning the properties 

 and composition of the aqueous humor. It is perfectly color- 

 less and transparent, faintly alkaline, of a specific gravity of 

 about 1,005, 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 is not rendered turbid by heat or other agents 

 which coagulate albumen. Yarious inorganic salts, the chlo- 

 rides, sulphates, phosphates, and carbonates, exist in this 

 liquid, in small proportion. 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, structure- 

 less capsule, called the hyaloid membrane, which is about 

 s-fl 1 ^ of an inch in thickness. This inmbrane adheres pretty 

 strongly to the limitary membrane of the retina. In front, 



