INTRACRANIAL AND INTRAOCULAR FLUIDS 



I 76") 







fig. 4. An arachnoid villus 

 which has invaded the dura and 

 protrudes into the sagittal sinus. 

 The villus may be seen as an out- 

 growth of the loose cellular tissue 

 of the arachnoid membrane. 

 [From Scholz & Ralston (202) 



'Er/NA 

 CHOROO 

 'SCLERA 



fio. 5. Anteroposterior section of the human eye. [From 

 Wolff (253).] 



The circulation is a dual one; the retinal circulation 

 is mediated by the central artery and vein of tin- 

 retina which enter the globe in company with the 

 optic nerve; the artery ramifies on the surface of 

 the retina and finally sends capillaries into the 



inner nervous layers of this tissue while the uveal 

 circulation, mediated by the ciliary arteries, and the 

 anterior > i1i.ua and vortex veins, enters and leaves 

 the globe independently of the optic nerve. The 

 long posterior and anterior ciliar) arteries anastomose 

 to form an arterial circle in the ciliary bod) the 

 greater circle of the iris. The ramifications of this 

 uveal system constitute the middle vascular coat of 

 the eye; posteriorly, the capillary network derived 

 from the ciliary arteries is called the choriocapillaris 

 and constitutes the nutritional pathway for the outer 

 layers ol the retina. Exchanges between blood and 

 vitreous body will clearly take place both from the 

 choriocapillaris and from the capillary networks de- 

 rived from the retinal artery. More anteriorly, the 

 ramifications of the meal system give rise to the 

 capillary supplies of the ciliary body and the iris. 

 The venous return from the choroid, the iris and the 

 ciliary processes is by way of four large vortex veins, 

 while the anterior ciliary veins drain the blood from 

 the ciliary muscle and from the series of plexuses in 

 the neighborhood of the cornea (p. 1766). 



The structure of immediate concern is the ciliary 

 body; essentially it is made up of the ciliary muscle, 

 concerned with accommodation, and some 80 ciliary 

 processes (fig. 7) projecting into the posterior cham- 

 ber; each process is supplied by an arterial branch 

 from the major circle of the iris which ramifies in 

 the process into a tangle of capillaries reminiscent of 



