SUBCLAVIAN VEINS. 965 



Tributaries. (a) A vein from the cochlea and (6) the inferior petrosal sinus- join 

 it near its commencement, (c) Pharyngeal branches from the venous plexus on the wall 

 of the pharynx, (d) Emissary veins from the cavernous sinus, (e) The common facial 

 vein, which receives the anterior and posterior facial veins. (/) The lingual veins, which 

 return part of the blood from the tongue, (g) The vena comitans hypoglossi, which 

 accompanies the hypoglossal nerve, (h) The superior thyreoid vein, which accompanies 

 the corresponding artery, (i) The middle thyreoid vein, which passes backwards from 

 the corresponding lobe of the thyreoid gland and crosses the middle of the lateral aspect of 

 the common carotid artery. (J) The occipital vein occasionally terminates in the internal 

 jugular vein. In many cases, however, it ends in the sub-occipital plexus, which is 

 drained by the vertebral and deep cervical veins (see p. 963). 



The common facial vein is formed by the union of the anterior and posterior facial 

 veins. It accompanies the first part of the external maxillary artery in the carotid 

 triangle, and terminates in the anterior border of the internal jugular vein. Just before 

 it disappears beneath the sterno-mastoid, the common facial vein frequently gives off a 

 large branch which descends along the anterior border of the sterno-mastoid to the 

 supra-sternal fossa, where it joins the anterior jugular vein. 



The anterior facial vein (Fig. 785) commences at the medial commissure of the eye- 

 lids as the angular vein, which is formed by the union of the supra-orbital and frontal 

 veins. It passes downwards and backwards, in the face, to the lower and anterior part 

 of the masseter muscle, which it crosseSj lying in the same plane as the external maxillary 

 artery, but following a much straighter course. After crossing the lower border of the 

 mandible it passes across the submaxillary triangle, superficial to the submaxillary gland, 

 and separate from the external maxillary artery, which there lies in a deeper plane. It 

 terminates, a short distance below the angle of the mandible, by uniting with the posterior 

 facial vein to form the common facial vein. 



The anterior facial vein receives tributaries corresponding with all the branches of 

 the external maxillary artery, ex,cept the ascending palatine and the tonsillar, which have 

 no accompanying veins, the blood from the region which they supply being returned for 

 the most part through the pharyngeal plexus. The anterior facial vein also communicates 

 with the pterygoid plexus around the external pterygoid muscle, by means of an 

 anastomosing channel, called the deep facial vein, which passes posteriorly, between 

 the masseter and buccinator muscles, into the infra-temporal fossa. 



The posterior facial vein, see p. 968. 



The inferior thyreoid veins have already been described (see p. 964). 



Venae Subclaviae. The subclavian vein, of each side, is the direct continua- 

 tion of the main vein of the upper extremity, i.e. the axillary vein ;* but through 

 its tributary, the external jugular vein, it receives blood both from the head and 

 from the superficial parts of the neck. 



From its commencement, at the external border of the first rib, it runs medially, 

 below and anterior to the corresponding artery from which it is separated by 

 the lower part of the scalenus anterior muscle, and it terminates, behind the 

 medial end of the clavicle, in the innominate vein of the corresponding side. As 

 it passes medially it forms a slight curve, the convexity of which is directed 

 upwards. 



Each subclavian vein possesses a single bicuspid valve which is situated imme- 

 diately to the distal side of the opening of the external jugular vein. 



Relations. The subclavian vein is in relation anteriorly with the posterior layer of 

 the costo-coracoid membrane, which separates it from the subclavius muscle, and the 

 nerve to the subclavius, and with the back of the medial end of the clavicle, from which 

 t is partly separated, however, by the fibres of the sterno-hyoid and sterno-thyreoid 

 muscles. 



It is closely attached, anteriorly, to the posterior surface of the costo-coracoid 

 membrane ; consequently it is expanded when the clavicle is moved forwards, an arrange- 

 ment which constitutes a distinct danger when operations are being performed in the 

 neighbourhood of the vein ; for, in the event of the vessel being wounded, forward 

 movement of the clavicle may cause air to be sucked into the vein, with fatal results. 



Posterior to the vein, and on a higher plane, is the first part of the subclavian artery, 

 but it is separated from the second part by the scalenus anterior. As soon as it reaches 

 the medial border of the anterior scalene the subclavian vein unites with the internal 

 jugular vein, immediately anterior to the internal mammary artery. 



