658 



THE BLOOD-VASCULAR SYSTEM 



vestibuli, into the inferior petrosal sinus. Some also passes through the vena 

 canaliculi cochleae which traverses the canal of the same nam.e and empties into 

 the commencement of the internal jugular vein. 



6. THE VEINS OF THE ORBIT 



The blood from the eyeball and orbit is returned by the superior ophthalmic 

 vein into the cavernous sinus. This vein and its tributaries have no valves, and 

 communicate with the frontal, supraorbital, inferior cerebral, and other veins. 

 Hence under certain conditions, as from pressure on the cavernous sinus, the blood 



Fig. 521. — The Veins of the Orbit. 



Supraorbital artery 



Lacrimal gland 



Superior rectus, cut 



Eyeball 



Lateral rectus 

 Lacrimal artery 



Superior rectus, cut 

 Inferior ophthalmic vein 

 Superior ophthalmic vein 



Optic nerve 

 Superior ophthalmic vein 



Commencement of superior 

 ophthalmic vein 



Reflected tendon of superior 



oblique 

 Ophthalmic artery 



Anterior ethmoidal artery 



Posterior ethmoidal artery 

 Ciliary arteries 



Levator palpebrae, cut 



Annulus communis of Zinn 

 Ophthalmic artery 



Optic chiasma 



Internal carotid artery 



may flow in the contrary direction to the normal — i. e., from behind forward into 

 the frontal and supraorbital, and thence through the angular vein into the anterior 

 facial; or upward into the cerebral venous system. In this way pressure on the 

 retinal veins is quickly relieved, and little or no distension occurs in cases of 

 obstruction in the cavernous sinus. 



The superior ophthalmic vein [v. ophthalmica superior] begins at the medial 

 angle of the eyelid by a free communication with the frontal, supraorbital, and 

 angular veins, and thence runs backward and laterally with the ophthalmic 

 artery across the optic nerve to the medial end of the superior orbital (sphenoidal) 

 fissure, where it is usually joined by the inferior ophthalmic vein. It then passes 

 backward between the two heads of the lateral rectus muscle below the sixth 

 nerve, leaves the orbit through the medial end of the superior orbital (sphenoidal) 

 fissure and enters the front part of the cavernous sinus. In this course it lies 

 anterior and superficial to the ophthalmic artery. 



Tributaries. — ^(1) The naso-frontal vein; (2) the superior muscular veins; (3) 

 the veins of the lids and conjunctiva; (4) the ciliary veins; (5) the anterior and 

 posterior ethmoidal veins; (G) tlie lacrimal vein; (7) the central vein of the 

 retina; and (8) the inferior ophthalmic vein. 



(1 ) The naso-frontal vein fv. iiaso-fronf alis] begins by a free communication with the supra- 

 orbital vein and onterw the orbit Ihrou^ih the front ;il notch or foramen. It frequently joins 

 the superior oplithahnic vein quite far back in tlie orbit (see fig. 520). 



(2; Tlie muscular veins [vv. muscularesj are derived from the levator palpebrae, superior 

 rectus, suncrirtr obliriue, and medial rectus. 



(3) Tlio palpebral and conjunctival veins [vv. palpebralos; vv. conjunctivales ant. et post.], 

 both anterior and pos(ori(jr, oi)(;n into the superior ophthidinic. 



(4) The ciliary veins, tiie veins of the eyeball, are divided into two sets. An anterior 

 [vv. ciliares ant.] emerge from the eyeball with the anterior ciliary arteries, and open 



