616 THE VETXS 



veins entering into this plexus are: — the two middle meningeal, which accom- 

 pany the artery of that name; the posterior dental vein ; the mandibular (inferior 

 dental) ; the masseteric ; tlie buccal ; the pterygoid veins from the pterygoid 

 muscles; the deep temporal, l»y which the plexus connnunicates with the tem- 

 poral plexus; the spheno-palatine vein; the infraorbital; the superior pala- 

 tine ; the lower brancli of the ophthalmic vein, which courses through the spheno- 

 maxillary fissure from the orbit; and the Vesalian vein, through which the plexus 

 comunicates with the cavernous sinus. The plexus ends posteriorly in the internal 

 maxillary vein which joins the common temporal vein, and anteriorly in the ante- 

 rior internal maxillary or deep facial vein, which passes forwards and downwards 

 between the buccinator and masseter muscles to join the facial vein. 



The above-mentioned veins, forming by their confluence the pterygoid plexus, 

 correspond in their course so nearly with that of their companion arteries, that a 

 detailed description is not necessary. Although deeply placed, they are for 

 convenience described with the superficial veins. 



The temporo-maxillary vein is formed by the union of the common temporal 

 vein and internal maxillary vein in the substance of the parotid gland. It usually 

 joins about the angle of the jaw the posterior auricular vein to form the external 

 jugular. At other times it divides into two branches, an anterior and a posterior. 

 The anterior division runs forwards and downwards, and joins the facial vein (see 

 Facial Vein). The posterior division runs backwards over the sterno-mastoid 

 and joins the posterior auricular to form the external jugular. When the temporo- 

 maxillary trunk without dividing joins the posterior auricular to form the external 

 jugular vein, the anterior branch is represented by the communicating branch 

 between the external jugular and facial veins. 



The Posterior Lateral Veins. — The posterior auricular vein begins in a venous 

 })lexus on the posterior part of the parietal bone. This plexus communicates with 

 the vein of the opposite side, across the sagittal suture, and with the posterior 

 branch of the superficial temporal vein in front, and with the occipital vein behind. 

 It descends over the back part of the parietal bone and the mastoid process of the 

 temporal bone, lying wdth its artery behind the ear. It then leaves the artery, 

 and passing over the upper part of the sterno-mastoid muscle obliquely forwards and 

 downwards, joins the temporo-mandibular vein al^out the level of the angle of the 

 lower jaw, forming the external jugular vein (fig. 385). 



Tributaries. — (a) Auricular veins from the back of the pinna; and (b) the 

 stylo-mastoid vein, corresponding to the little stylo-mastoid artery. The latter vein 

 opens into the posterior auricular vein, as a rule, as the latter leaves the mastoid 

 process. 



2. THE SUPERFICIAL VEINS OF THE XECK 



The external jugular vein is formed by the confluence of the posterior auricular 

 and temporo-maxillary veins near the angle of the lower jaw. It runs obliquely 

 downwards and backwards across the sterno-mastoid muscle to a spot opposite the 

 middle of the clavicle, where it terminates as a rule in the subclavian vein. A 

 line drawn from a point midway between the mastoid process and angle of the jaw 

 to the middle of the clavicle will indicate its course. It is covered by the skin, 

 superficial fascia, and platysma, and is crossed by a few branches of the cervical 

 plexus, the great auricular nerve running parallel to it at the upper part of the 

 neck. It at first crosses the sterno-mastoid obliquely, then runs nearly parallel to 

 the posterior border of that muscle, from which it is separated tln-oughout its 

 course by the anterior layer of the deep cervical fascia. 



-Just above the clavicle it perforates the cervical fascia, by Avhich it is prevented 

 from readily collapsing, the fascia being attached to its walls. It then opens into 

 the subclavian vein; occasionally into the internal jugular, or into the confluence 

 of the subclavian and internal jugular veins. It contains a pair of valves about one 

 inch to two inches above the clavicle, and a second pair where it enters the sub- 

 clavian vein. Both of these valves were shown by Sir James Struthers not to 

 prevent the blood regurgitating, or injections passing from the larger vein into the 

 external jugular. 



