82 ALLEN 



Rectus Vein (PL II, figs. 13 and 15; Rec.V.). — This ves- 

 sel arises from a ventral branch coming from the inferior rectus 

 muscle and a cephalic branch coming from the superior and 

 internal recti muscles. Its course is then dorsad between the 

 optic nerve and the superior rectus muscle, and it unites with the 

 ophthalmic and iris veins to form the internal jugular trunk. 

 The vein from the external rectus muscle empties into the iris 

 vein and will be described more fully in connection with that 

 vessel. 



Ophthalmic Veins (Pis. I and II, figs, i, 5, 13, 15 and 19; 

 Oph.V.). — Each of these veins carries off the venous blood, 

 which has become collected in the choroid sinus. This sinus 

 (PI. Ill, fig. 19 ; Chor.S.) is horse-shoe shaped, the anterior arm 

 being much longer than the posterior one. It lies between the 

 silver layer of the choroid and the similar shaped choroid ar- 

 tery, and occupying a large part of the space between the optic 

 nerve and the choroid gland, drains the entire choroid coat and 

 also the ventral portion of the iris. The venous blood from the 

 dorsal part of the iris is returned by the iris vein proper, w^hich 

 will be described later on. The capillaries in the choroid may 

 reach the choroid sinus in either of 2 ways. They may become 

 collected into the choroid veins (PI. Ill, fig. 21 ; Chor. V.), which 

 break up into a fine rete mirabile of venous capillaries which 

 run parallel with the arterial rete mirabile capillaries, and 

 these in turn become collected entad into larger venous vessels 

 that empty into the choroid sinus ; or they ma}' reach the cho- 

 roid sinus directly by what I have designated as the dorsal 

 choroid vein or the 2 ventral choroid veins (PI. Ill, fig. 19 ; 

 D.Chor.V. and V.Chor.V.), which empty into the anterior and 

 posterior horns respectively. The vein returning the venous 

 blood from the ventral portion of the iris is designated as the 

 ventral or minor iris vein (PI. Ill, fig. 19; Ir.V.^j)). This 

 vessel passes obliquely dorsad in the vascular layer of the 

 choroid, directl}' cephalad of the ramus ciliaris brevis, and 

 empties into the inner side of the anterior horn of the choroid 

 sinus. No similar arter}' was observed and it is probable that 

 the arterial supply for the ventral part of the iris comes from 

 the ventral choroid arteries rather than from the iris arter}-. 



