VITREOUS HUMOR. 437 



194.* Fig. 194 represents 



on the left, the retina, 

 with a portion of the op- 

 tic nerve attachea to it. 

 The external membrane 

 (tunica Jacobi) is turned 

 down, and the foramen of 

 Soemrnering instead of a 

 distinct hole, presents the appearance of a fold or depression 

 with elevated sides. The figure to the right, shows the retina 

 expanded over the vitreous humor, and the place may be 

 observed from which the optic nerve has been cut away, and 

 from which the vessels branch out. To the right of this is seen 

 the foramen of Soemrnering, represented as a black spot, sur- 

 rounded by a dark shade. 



Of the Humors of the Eye. 



The three humors of the eye, viz. the Aqueous, the Crys- 

 talline^ and the Vitreous, are separately invested with a 

 membranous capsule, which is very delicate, and perfectly 

 transparent. 



The Vitreous Humor 



Occupies almost all the cavity of the eye which is posterior 

 to the iris. It of course possesses a spherical form. It has a 

 depression in the centre of its anterior surface, in which the 

 posterior surface of the crystalline lens is received. It is 

 covered by the retina as far as the retina extends. 



The peculiar consistence of this body, which resembles that 

 of melted glass, is owing to its membrane ; which is a spheri- 

 cal sac, divided by many septa, or partitions, that form small 

 irregular cavities, in which a fluid is contained. This mem- 

 branous sac is most perfectly transparent, and very flexible ; it 

 has, however, some strength ; as it will support the weight of 

 all the fluid it contains, and may be suspended from a hook or 

 forceps. The fluid may be separated from the membranes, 

 by beating the vitreous humor in a cup with a spoon : or by 

 37* 



