XASAL—A URICULAR—OPHTHA LMIC 625 



The Veins of the Medulla and Pons 



The veins from the medulla oblongata and the pons terminate in the inferior 

 petrosal and lateral sinuses. 



4. THE VEINS OF THE NASAL CAVITIES 



The venous plexuses on the inferior turbinated bone and back of the septum 

 are described with the Nose. The veins leaving the nasal cavities follow roughly 

 the course of their corresponding arteries. Thus the spheno-palatine veins pass 

 tlirough the spheno-palatine foramen into the pterygoid plexus; the anterior and 

 l^osterior ethmoidal veins join the ophthalmic. Small veins accompany branches of 

 the facial artery through the nasal bones and nasal processes of the superior 

 maxillary bones, and end in the angular and facial veins; and other small veins pass 

 from the nose anteriorly into the superior labial, and thence to the facial. 



5. THE VEINS OF THE EAR 



The veins from the external ear and external auditory meatus join the temporal 

 and posterior auricular veins. The veins from the tympanum open into the 

 suijcrior petrosal sinus and temporo-maxillary vein. The blood from the labyrinth 

 flows chiefly through the internal auditory veins which lie with the internal 

 auditory artery in the internal auditory meatus, and enters the inferior petrosal or 

 lateral sinus. Some of the blood from the labyrinth, however, passes through the 

 vestibular vein which lies in the aqueductus vestibuli, into the inferior petrosal 

 -inus, and some through the aqueductus cochlese, 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 ophthalmic vein into 

 tlie cavernous sinus. This vein and its tributaries have no valves, and communi- 

 cate in front with the frontal, supraorbital, and other veins. Hence under certain 

 conditions, as from pressure on the cavernous sinus, the blood may flow in the 

 contrary direction to the normal — i. e. from behind forwards into the frontal and 

 supraorbital, and thence through the angular vein into the facial. In this way 

 I)ressure on the retinal veins is quickly relieved, and little or no distension occurs 

 in cases of obstruction in the cavernous sinus. 



The ophthalmic vein, or common ophthalmic vein, is formed by the 

 confluence at the back of the orl)it of the superior and inferior ophthalmic veins. 

 It is a short thick trunk, and passes backwards between the two heads of the 

 external rectus muscle below the sixth nerve, and at the inner part of the 

 sphenoidal fissure leaves the orbit and enters the front part of the cavernous sinus. 



A. The superior ophthalmic vein, larger than the inferior, begins at the 

 inner canthus of the eyelid by a free communication with the frontal, supra- 

 orbital, and angular veins, and thence runs backwards and outwards with the 

 ophthalmic artery across the optic ner\'e to the inner end of the sphenoidal 

 fissure, Avhere it joins the inferior ophthalmic vein to form the common ophthalmic 

 trunk. In this course it lies anterior and superficial to the ophthalmic artery. 



Tributaries. — (1) The superior muscular veins; (2) the ciliary veins; (3) the 

 anterior and posterior ethmoidal veins; (4) the lachrymal vein; and (5) the central 

 vein of the retina. 



(1) The superior muscular branches are derived from the levator palpel)rse, 

 superior rectus, superior oblique and internal rectus. 



(2) The ciliary veins are divided into two sets: an anterior, which emerge 

 from the evel)all with the anterior ciliary arteries, and open into the muscular veins 

 returning the blood from the four recti; and a posterior set, known as the venae vor- 



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