MAMMALS 



473 



with, branches of the anterior cihary arteries witli shunt-hke vessels 

 which can be opened or closed by large epithelioid cells. In the 

 Primates, as we have seen, the ciliary cleft is obliterated by the great 

 development of the ciliary muscle, thus cutting off the possibility of tJie 

 drainage of aqueous by this route ; to maintain connections with the 

 anterior chamber a sj^ecial sinus, the caxal of schlemm, is thus 

 developed as a diverticulum from the intrascleral venous plexus, 



Figs. 611 and 612. — The Drain.\ge Channels from the Angle of the 

 Anterior Chamber in Placentals. 



A,V. A.C.V. 



C.B. C.S.S. 



CB. V.P 



Fig. 611. — A lower Placental (rabbit) 



Fig. 612. — A higber Placental (Primate). 



ACV, anterior ciliary veins ; ..41^, acjueous vein ; C, cornea ; CB, ciliary 

 body ; CSS, ciliary cleft ; EV, efferent ciliary veins ; /, iris ; IP, intra- 

 scleral ciliary plexus ; .S', sclera ; SC, canal of Schlemm ; T, trabeculte 

 traversed by a canal of Sondermann ; IP, ciliary venous plexus. 



In Fig. 611 the essential drainage is from the anterior chamber into the 

 ciliary cleft, thence through the intrascleral plexus of veins into the anterior 

 ciliary veins. In Fig. 612 tlie older channels are represented as in Fig. 611 

 draining from the ciliary venous plexus, but superimposed on this is a new 

 drainage system represented by Sondermann's canals, the canal of Schlemm, 

 an anterior extension of the intrascleral venous plexus, together with the 

 intra.scleral and aqueous veins emptying directly into the anterior ciliary veins. 



placed anteriorly at the corneo-scleral junction at which level the angle 

 of the anterior chamber is now closed (Fig. 612). This structure, which 

 may branch to have more than one lumen and is lined by a single layer 

 of endothelium, runs circumferentially around the globe separated from 

 the anterior chamber by the corneo-scleral trabecidse through which 

 pass minute channels, the canals of Sondermann (1933), and is con- 

 nected to the intrascleral venous plexus by numerous efferent channels, 

 some of which reach the subconjunctival region directly as aqueous 

 veins. This system, added to the intrascleral venous plexus to com- 

 pensate for the closure of the ciliary cleft, plays the major part in the 

 drainage of the aqueous humour in the eyes of Primates. 



