60 ALLEN 
cephalic artery is the zzfundibular artery (Pl. III, fig. 25; Inf.- 
A.). This vessel, which is given off caudad to the hypophysis 
and infundibulum, sometimes arises from either of the pos- 
terior cerebral arteries close to their origin from the encephalic 
artery. 
Orbito-nasal Arterzes (Pls. I, II and III, figs. 1, 5, 13, 17 
and 18; O:N.A.).— These vessels which are the cephalic 
branches of the internal carotid arteries, pass forward along 
the dorso-lateral surface of the parasphenoid. While still within 
the eye-muscle canal each orbito-nasal artery runs below the 
recti muscles, giving off several small branches to the superior, 
inferior, and internal recti muscles. Shortly after reaching 
the orbit, what I have designated as the rectus artery (Pl. I, 
fig. 13; Rec.A.) arises between the internal and the inferior 
recti muscles, giving off at first a small branch to the outer 
surface of the internal rectus muscle; then dividing, one branch 
continues caudad between the external and internal recti mus- 
cles; while the other branch curves laterad a short distance 
and in turn bifurcates, one branch going dorsad to the superior 
rectus muscle, and the other to the inferior rectus muscle. The 
main orbito-nasal trunk, continuing cephalad, passes behind 
the internal rectus muscle to which it sends several vessels; 
and in the anterior part of the orbit passes between, but lat- 
erad to the oblique muscles, giving off a dorsal branch to 
the superior oblique muscle, and in the specimen from which 
fig. 13 was drawn, 2 ventral branches for the inferior ob- 
lique muscle. As has already been mentioned, the blood 
supply for the external rectus muscle comes largely from the 
iris artery, which is a branch of the external carotid artery. 
Together with the orbito-nasal vein and the olfactory nerve, 
the orbito-nasal artery passes out of the orbit through the olfac- 
tory foramen in the prefrontal bone. In passing through this 
foramen and cephalad of it, the vein lies mesad of the nerve, 
and the artery lies ventrad to both vein and nerve. Soon after 
leaving the orbit the orbito-nasal artery gives off at least 2 
dorso-cephalic vessels, the xasal sac arterzes (Pl. II, figs. 17 
and 18; N.S.A..,)). These small vessels at first pass behind and 
above the olfactory nerve to supply the dorsal radial filaments 
