366 NORMAL HISTOLOGY. 



The venous vessels of the eyeball culminate in two principal 

 sets, the posterior and anterior ciliary veins. The former, or the 

 venae vorticosae, collect the blood from the iris, the ciliary processes, 

 part of the ciliary muscle, and the choroid, and on emerging from 

 the sclera receive also the episcleral veins ; they, therefore, drain the 

 entire territory supplied by the ciliary arteries, except a part of the 

 region nourished by the anterior ciliary arteries. 



The lymphatics of the eyeball constitute the anterior and pos- 

 terior lymph-tracts, which do not comprise definite lymphatic 

 vessels, but a series of intercommunicating lymph-spaces varying in 

 size from the microscopic tissue-spaces to the anterior chamber. 



The anterior lymph-tract includes : 



1. The systems of the lymph-spaces within the cornea and the 

 sclera. 



2. The anterior chamber of the eye, containing the aqueous 

 humor, which possesses in small number the usual histological ele- 

 ments of lymphatic fluid, the leucocytes. The anterior chamber com- 

 municates with the posterior chamber through the cleft between the 

 iris and the lens, and indirectly, by means of the spaces of Fontana, 

 with the canal of Schlemm. 



3. The canal of Petit, connected by means of the interfascicular 

 clefts with the posterior chamber, and thus indirectly with the ante- 

 rior, these three spaces standing in close relation. 



The posterior lymph-tract includes two groups, the lymphatics 

 of the retina and of the vitreous body and those of the pericho- 

 roidal space. 



The constituents of the first group are : 



1. The hyaloid canal of the vitreous, which empties into the 

 lymph-clefts of the optic nerve. 



2. The perivascular lymph-channels surrounding the retinal 

 vessels, which likewise pour their contents into the lymph-spaces of 

 the nerve. 



3. The lymph-clefts of the optic nerve, terminating within the 

 subarachnoidean space of its sheaths. 



The perichoroidal space, lying between the scleral and the 

 choroid coat, drains the choroid and communicates with the sac 

 enclosed by Tenon's capsule ; the perivascular lymphatics sur- 

 rounding the venae vorticosae lead from the perichoroidal cleft into 

 Tenon's space, from which channels connect with the supra- vaginal 

 space, embracing the optic nerve ; finally, communications exist 

 between this space and the great intercranial lymphatic cavities. 

 Connections between the lymph-clefts of the optic nerve and the 

 perichoroidal space probably also exist in the vicinity of the optic 

 entrance. 



