6o ALLEN 



cephalic artery is the infiindibtilar artci'y (PI. Ill, fig. 25 ; Inf.- 

 A.). This vessel, which is given off caudad to the hypoph^'sis 

 and infundibulum, sometimes arises from either of the pos- 

 terior cerebral arteries close to their origin from the encephalic 

 artery. 



Orbito-nasal Arteries (Pis. I, II and III, figs, i, 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. Shortl}' after reaching 

 the orbit, what I ha\'e designated as the rccttis artery (PI. II, 

 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* ^3 ^'^^s 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 bolli vein and nerve. Soon after 

 leaving the orbit the orbito-nasal artery gives off at least 2 

 dorso-cephalic vessels, the nasal sac arteries (PI. Ill, figs. 17 

 and 18 ; N.S. A.^^). These small vessels at first pass behind and 

 above the olfactory nerve to supply the dorsal radial fihiments 



