THE SUPERIOR CAVAL SYSTEM. 879 



The inferior cerebellar veins (vv. cerebelli iuferiores), somewhat larger than 

 the superior, pass in part forward and outward to open into the lateral or superior 

 petrosal sinuses, and in part backward to unite with the occipital sinus. 



The Ophthalmic Veins. 



The ophthalmic veins take their origin from the contents of the orbit and pass from 

 before backward, uniting to form two principal trunks, a large superior and a smaller 

 inferior ophthalmic vein, which open at the sphenoidal fissure into the anterior 

 extremity of the cavernous sinus. At the margin of the orbit both veins form 

 important connections with the angular vein, and, since no valves occur in any of 

 the branches of the ophthalmic veins, they form important emissaries connecting 

 the cavernous sinus with the facial vein. 



1. The Superior Ophthalmic Vein. — The superior ophthalmic vein (v. oph' 

 thalmica superior) (Fig. 757) is formed at the inner angle of the orbit by the fusion of 

 usually two vessels which come from the supra-orbital and angular veins and pass 

 respectively above and below the pulley of the superior oblique muscle of the eye 

 and unite a short distance posterior to that structure. The anterior portion of the 

 superior ophthalmic vein so formed is sometimes termed the v. naso-froiitalis, and in 

 its further course it is directed somewhat tortuously, at first obliquely backward and 

 outward, passing across the optic nerve and beneath the superior rectus muscle, 

 and then more directly backward to the sphenoidal fissure. 



Tributaries. — The superior ophthalmic receives numerous tributaries from both the eyeball 

 and the other contents of the orbit, most of the branches from the latter sources corresponding 

 to branches of the ophthalmic artery. Thus it receives (a) the anterior and {b) the posterior 

 ethmoidal veins (vv. ethmoidales anterior et posterior) which return blood from the sphenoidal 

 sinus and the superior meatus and turbinate bone of the nose, communicating with the other 

 veins of the nasal cavity and entering the orbit by the ethmoidal foramina ; (f) the lachrymal 

 vein (v. lacrimalis), a vein of considerable size arising in the lachrymal gland and accompanying 

 the artery of the same name ; and {d) muscular veins (vv. musculares) which return the blood 

 from the levator palpebrae superioris, the superior and internal recti, and the superior oblique, the 

 veins from the other muscles of the orbit usually opening into the inferior ophthalmic vein. 



From the eyeball it receives {e) the two superior venae vorticosae. These veins return the 

 blood from the choroid coat, the ciliary body, and the iris, and are four in number, each having 

 its origin from a rich plexus which occupies one of the four quadrants of the choroid, the prin- 

 cipal stems of the plexus radiating from all directions towards the central point of its quadrant. 

 Here they unite to form a single trunk which pierces the sclera obliquely at about the equator 

 of the eyeball, the veins from the two superior quadrants emptying into the superior ophthalmic, 

 while the two from the inferior quadrants connect with the inferior ophthalmic. Occasionally 

 five or six venae vorticosae exist, and they open sometimes into the muscular veins instead of 

 directly into the ophthalmic stems. (/) The anterior ciliary veins (vv, ciliares anteriores) are 

 very slender veins which leave the eyeball at the points where the recti muscles are inserted 

 into the sclerotic ; two or three veins are associated with each muscle-tendon and open into the 

 muscular veins, [g) The posterior ciliary veins (vv, ciliares posteriores) accompany the poste- 

 rior or short ciliary arteries. The territory supplied by the arteries is, however, drained by the 

 venae vorticosae, and the posterior ciliary veins, which are very small, take their origin only from 

 the posterior portion of the sclerotic and from the sheath of the optic nerve, {h) The vena cen- 

 tralis retinae is a single stem which accompanies the corresponding artery through the centre of the 

 optic nerve, and has its origin in branches which ramify over the surface of the retina. The vein 

 leaves the optic nerve usually before the artery and opens either into the superior ophthalmic 

 vein or, more frequently, directly into the cavernous sinus. 



2. The Inferior Ophthalmic Vein. — The inferior ophthalmic vein (v. oph- 

 thalmica inferior) (Fig. 757) takes its origin from a net- work of small veins situated 

 on the inner portion of the floor of the orbit near its border. This plexus communi- 

 cates with the facial vein and is continued backward towards the fundus of the orbit, 

 more frequently as a coarse net-work than as a definite stem. The vein, when it 

 exists, or the net-work, anastomoses with branches of the superior ophthalmic. 



Tributaries. — (a) Muscular branches from the inferior and external recti and the inferior 

 oblique muscles and {b) the inferior venae vorticosae from the lower half of the eyeball. 

 It opens posteriorly either directly into the cavernous sinus or else unites with the superior 

 ophthalmic vein. 



