82 ALLEN 
frectus Vein (P1. Il, figs. 13 and 15; Rec.V.).— This ves- 
sel arises from a ventral branch coming from the inferior rectus 
muscle and acephalic 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 (Pls. I and II, figs. 1, 5, 13, 15 and 19; 
Oph.V.). — Each of these veins carries off the venous blood, 
which has become collected in the chorozd senus. This sinus 
(Pl. III, 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, which 
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 chorozd vezns (PI. III, 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 may reach the cho- 
roid sinus directly by what I have designated as the dorsal 
choroid vein or the 2 ventral choroid veins (Pl. III, 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 tris vei (Pl. Ill, fig. 19; Ir.V.,)). This 
vessel passes obliquely dorsad in the vascular layer of the 
choroid, directly cephalad of the ramus ciliaris brevis, and 
empties into the inner side of the anterior horn of the choroid 
sinus. No similar artery 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 artery. 
