1766 HANDBOOK OF PHYSIOLOGY ^NEUROPHYSIOLOGY III 



fig. 6. The circulation of the 

 Iniin.m eye. O.A., ophthalmic ar- 

 tery; MB, muscular branch, 

 A.C.A., anterior ciliary artery; 

 S.P.C., short posterior ciliary ar- 

 tery; PC. A., posterior ciliary ar- 

 tery; CAR., central artery of the 

 retina; R.A., retinal artery; V.V., 

 vortex vein; I.O.V., inferior or- 

 bital vein; A.B., anastomosing 

 branch; C.S., cavernous sinus. 

 [From Duke-Elder (75).] 



IX. A. 



VV. 



a glomerular tuft (21) and is covered by a double 

 layer of epithelium, the outer layer of cells being 

 pigmented. The ciliary processes obviously represent 

 a region of expanded surface area — Baurmann cal- 

 culated that, in man, the area was some 6 cm 2 — and 

 for this reason at least may be looked on as the source 

 of the aqueous humor, although, as with the choroid 

 plexuses, the evidence favoring this view is not un- 

 equivocal. 



Drainage of the aqueous humor takes place by 

 way of the canal of Schlcmm into the venous system 

 (fig. 8); the canal of Schlemm is a channel lying in 

 the sclera at the corneoscleral junction. The wall 

 of the canal consists of a delicate layer of endothelium; 

 between the anterior chamber and this delicate 

 membrane is the corneoscleral meshwork made up of 

 a series of collagenous lamellae and rods, and the 

 aqueous humor must pass through the spaces in this 

 meshwork the spaces of Fontana- in order to 

 reach the canal. From the canal the fluid is carried 

 by collectors into the vessels of the intrascleral venous 

 plexus which is the deepest of four plexuses de- 

 scribed by Maggiore (149) in the anterior segment of 

 the eye 'tig. 8). From this plexus, blood, diluted with 

 aqueous humor, is carried more superficially in the 

 episcleral and conjunctival veins to empty finally in 

 the .interior ciliary veins. That the intraocular fluid 

 was, indeed, drained away in this fashion was made 

 ver\ probable by I.aulier's (140) observation that the 

 blood from the anterior ciliary veins was considerably 

 diluted by comparison with blood from an ear 

 vein; later Seidel (206) showed thai colored solu- 

 tions, introduced into the anterior chamber, appeared 

 rapidly in the anterior ciliary veins even when the 



intraocular pressure was held below normal. Seidel's 

 work demonstrated very clearly that drainage by 

 way of the canal of Schlemm was possible, and his 

 careful measurements of the pressure in the anterior 

 ciliary veins showed that there was a sufficient gradi- 

 ent of pressure between the anterior chamber and the 

 venous system to permit a continuous flow. Un- 

 fortunately, Lauber*s and Seidel's work was either 

 ignored or dismissed by subsequent workers, e.g. 

 Duke-Elder (76), so that the view that the aqueous 

 humor was a stagnant fluid was maintained for some 

 time. However, the discovery by Ascher (4 (ii that 

 drainage was not confined to an emptying into the 

 deep intrascleral vessels but could occur directly into 

 the more superficial episcleral and conjunctival veins, 

 along what he called aqueous veins, re-established 

 Seidel's view. Ascher observed among the superficial 

 vessels of the globe what appeared to be empty veins; 

 a careful study indicated, however, that they con- 

 tained aqueous humor and, on following them periph- 

 eral-wards, they could usually be seen to empty into 

 blood-filled veins, in which ease it frequently hap- 

 pened that the two currents did not mix immedi- 

 ately but remained separate to give a laminated 



aqueous vein (lit; g) Subsequent mikK of these ves- 

 sels by a ureal many workers 7 has fullv continued 



'The literature relating c c > the aqueous veins is verj largi 

 and repetitive. Goldmann (105, 106, 109) provided the un- 

 equivocal proof that the veins contained aqueous humor In 

 injecting fluorescein into the blood While the blood-veins 

 fluoresced strongly, the aqueous wins did do! because fluores- 

 cein penetrates only very slowly into the aqueous humor. I hom- 



aSSCn (Ml) showed that in .1 human eye, the introduction of 



methylene blue mi" the anterioi chambet caused the aqueous 



