THE VITREOUS HUMOUR. 74 1 



of the retina {Henlc, Iivanoff). From here forwards lying between both, are the meridional 

 fibres of the zonule, which are united with the surface of the vitreous and the ciliary processes. 

 A part of the fibrous layer bends into the saucer-shaped depression, and bounds it. A canal, 

 2 mm. in diameter, runs from the optic papilla to the posterior surface of the capsule of the 

 lens ; it is called the hyaloid canal, and was formerly traversed by blood-vessels. The peri- 

 pheral part of the vitreous humour is laminated like an onion, the middle is homogeneous ; in 

 the former, especially in the foetus, are round fusiform or branched cells of the mucous tissue 

 of the vitreous, while in the centre there are disintegrated remains of these cells {Iwanoff). The 

 vitreous humour contains a very small percentage of solids, 1*5 per cent, of mucin, [and, 

 according to Picard, there is 0*5 per cent, of urea, and about "75 of sodic chloride], 



[Structure. The vitreous humour consists essentially of mucous tissue, in whose meshes lies 

 a very watery fluid, containing the organic and inorganic bodies in solution. According to 



Fig. 523. 

 Horizontal section of the entrance of the optic nerve and the coats of the eye. a, inner, h, 

 outer layers of the retina ; c, choroid ; d, sclerotic ; e, physiological cup ; /, central artery 

 of retina in axial canal ; g, its point of bifurcation ; h, lamina cribrosa ; I, outer (dural) 

 sheath ; m, outer (subdural) space ; n, inner (subarachnoid) space ; r, middle (arachnoid) 

 sheath ; p, inner (pial) sheath ; i, bundles of nerve-fibres ; Jc, longitudinal septa of con- 

 nective-tissue. 



Younan, the vitreous contains two types of cells (1) amoeboid cells of various shapes and 

 sizes. They lie on the inner surface of the lining hyaloid membrane and the other mem- 

 branes in the cortex of the vitreous ; (2) large branching multipolar cells. The vitreous is 

 permeated by a large number of transparent, clear, homogeneous hyaloid membranes, which 

 are so disposed as to give rise to a concentric lamination. The canal of Stilling represents in 

 the adult the situation of the hyaloid artery of the foetus. It can readily be injected by a 

 coloured fluid.] 



The lymphatics of the eye consist of an anterior and a posterior set. The anterior consist of 

 the anterior and posterior chambers of the eye (aqueous), which communicate with the lym- 

 phatics of the iris, ciliary processes, cornea, and conjunctiva. The posterior consist of the 

 Eerichoroidal space between the sclerotic and the choroid (Schwalbe). This space is connected 

 y means of the perivascular lymphatics around the trunks of the vasa vorticosa, with the large 

 lymph-space of Tenon, which lies between the sclerotic and Tenon's capsule. Posteriorly, this 

 is continued into a lymph-channel, which invests the surface of the optic nerve ; while 

 anteriorly it communicates directly with the sub-conjunctival lymph-spaces of the eyeball. 

 The optic nerve has three sheaths (1) the dural ; (2) the arachnoid ; and (3) the pial sheath, 

 derived from the corresponding membranes of the brain. Two lymph-spaces lie between these 

 three sheaths the subdural space between 1 and 2, and the subarachnoid space between 2 

 and 3 (fig. 509). Both spaces are lined by endothelium ; and the fine trabeculae passing from 



