968 THE VASCULAE SYSTEM. 



It generally receives the mastoid emissary vein ; one of its tributaries receives 

 the parietal emissary vein, and occasionally an emissary vein from the confluens 

 sinuum (O.T. torcular Herophili) opens into it. 



THE VEINS OF THE ORBIT, THE NOSE, AND THE INFRA-TEMPORAL EEGION. 



The veins of these three regions are closely associated together ; for although 

 the orbital blood is returned, for the most part, to the cavernous sinus, by the 

 ophthalmic vein, the latter vein is closely connected with the pterygoid plexus, 

 which lies in the infra-temporal region. 



Veins of the Orbit. The veins of the orbit correspond, with the exception of 

 the naso-frontal vein, with the branches of the ophthalmic artery, and they 

 gradually converge, as they pass backwards in the orbit, until they form two main 

 trunks, a superior ophthalmic vein and an inferior ophthalmic vein. The two trunks 

 terminate separately, or by a single stem, in the anterior end of the cavernous 

 sinus, to which they pass through the superior orbital fissure, and between the 

 two heads of the lateral rectus muscle. 



The superior ophthalmic vein communicates, at the super o-medial angle of the 

 orbit, with the angular vein, and it receives the naso-frontal vein which accompanies 

 the frontal nerve. The inferior ophthalmic vein communicates, through the inferior 

 orbital fissure, with the pterygoid plexus. 



Veins of the Nose. The veins of the walls of the nasal cavity end partly in 

 the ethmoidal tributaries of the superior ophthalmic vein, partly in the septal 

 affluent of the superior labial and in the lateral nasal veins, both of which are 

 tributaries of the anterior facial vein ; but the majority of the veins of the nose, 

 both from the septal and lateral walls, join together to form a spheno-palatine 

 vein which passes through the spheno-palatine foramen and the pterygo-palatine 

 fossa, and terminates in the pterygoid plexus. 



Plexus Pterygoideus and the Vena Maxillaris Interna. The pterygoid plexus 

 of veins lies in the infra- temporal and pterygoid fossse. It covers the lateral 

 surface of the internal pterygoid muscle, and surrounds the external pterygoid. 

 It receives tributaries which correspond with and accompany the branches 

 of the internal maxillary artery viz., spheno-palatine, pharyngeal, vein of pterygoid 

 canal, infra-orbital, posterior superior alveolar, descending palatine, buccinator, two 

 or three deep temporal, pterygoid, masseteric, and inferior alveolar veins, and the 

 middle meningeal vein. It communicates, superiorly, with the cavernous sinus 

 through the foramen ovale ; anteriorly with the inferior ophthalmic vein through 

 the inferior orbital fissure ; and between the masseter and the buccinator with the 

 anterior facial vein by the deep facial anastomosing branch. It also communicates 

 posteriorly and medially, on the medial side of the internal pterygoid, with the 

 pharyngeal plexus, and it terminates posteriorly in the internal maxillary vein. 



The internal maxillary vein is a short vessel which accompanies the first part 

 of the internal maxillary artery, between the spheno-mandibular ligament and the 

 neck of the mandible. Between the neck of the mandible and the antero-medial 

 surface of the parotid gland it joins the upper part of the posterior facial vein. 

 Occasionally the internal maxillary vein is double, and sometimes it is represented 

 by several channels. 



The posterior facial vein is formed, immediately above the zygomatic arch, by 

 the union of the superficial and middle temporal veins. It crosses the zygomatic 

 arch, dips deep to the upper part of the parotid gland, and, whilst lying between the 

 antero-medial surface of the gland and the posterior border of the mandible, it 

 receives the internal maxillary vein or veins. Then it descends, through the 

 substance of the parotid, and, emerging from its lower end at the angle of the 

 mandible, it passes forwards and downwards to unite with the anterior facial vein 

 in the formation of the common facial vein. 



Whilst it is in the substance of the parotid it gives off a comparatively large 

 branch, which emerges from the lower and posterior part of the gland and forms 

 one of the two commencing tributaries of the external jugular vein. 



