66 SPECIAL SENSES. 



at the ora serrata, as we have already seen, the hyaloid mem- 

 brane is thickened, and becomes continuous with the suspen- 

 sory ligament of the lens. 



The vitreous humor itself is gelatinous, of feeble con- 

 sistence, slightly alkaline in its reaction, with a specific grav- 

 ity of about 1,005. Upon section, there oozes from it a 

 watery fluid of a slightly mucilaginous consistence. This 

 humor is not affected by heat or alcohol, but 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 numerous little 

 cavities, and contains cells and leucocytes. It is also pene- 

 trated by a branch from the central artery of the retina, which 

 passes through its centre to ramify on the posterior 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 re- 

 gard 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 com- 

 partments, by processes penetrating from and connected with 

 the hyaloid membrane. The weight of authority is decidedly 

 in favor of a subdivision 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 in- 

 terfere with its transparency. 



Summary of the Anatomy of the Globe of the Eye. 

 For the intimate structure of the various coats of the eye, 



