884 HUMAN ANATOMY. 



behind the pinna, occasionally receiving the mastoid emissary vein, and terminates near 

 the angle of the jaw by uniting with the temporo-maxillary to form the external jugular. 



3. The Posterior External Jugular Vein. — The posterior external jugular 

 \'ein arises from the integument and muscles of the upper and back part of the neck, 

 just below the occipital region, and descends obliquely behind the sterno-cleido-mastoid 

 muscle to open into the external jugular just after it has crossed the muscle. 



4. The Suprascapular Vein. — The suprascapular vein (v. transversa scapulae) 

 is really a double vein, being represented by two vessels provided with valves which 

 accompany the suprascapular artery as its venae comites. They arise upon the 

 upper part of the dorsal surface of the scapula, pass over the transverse ligament of 

 that bone, and are continued inward, parallel with the clavicle and behind it, to open 

 into the external jugular near its termination or else directly into the subclavian. 

 Just before their termination the two venae comites unite to a single stem. 



The suprascapular vein is usually joined either at or near its termination by the 

 transverse cervical veins which form the venae comites of the transversalis colli artery. 

 These veins may also open, howe\'er, directly into the subclavian. 



5. The Anterior Jugular Vein. — The anterior jugular vein (v. jugularis 

 anterior) (Fig. 753) arises beneath the chin, upon the mylo-hyoid muscle, by branches 

 which come from the integument and superficial muscles of that region, communicating 

 with the submental branches of the facial. The vein passes almost vertically down the 

 neck resting upon the sterno-hyoid muscle a short distance lateral from the median line, 

 until it meets the anterior (inner) border of the sterno-cleido-mastoid near its sternal 

 attachment. There it makes an abrupt bend, passing almost horizontally outward 

 beneath the muscle to open into the external jugular immediately above its termination. 



The anterior jugular receives a communicating branch, occasionally of con- 

 siderable size, from the facial subcutaneous veins, and tributaries from the median 

 region of the neck also open into it ; it may also receive small branches from the larynx 

 and thyroid gland. 



It contains no valves. At its origin it is superficial to the deep cervical fascia, but 

 below the hyoid bone it is embedded in the superficial layer of that fascia, and below 

 lies in the spatium suprasternale (space of Burns) formed by the splitting of the fascia 

 into two lamellae. In this space there occurs a transverse anastomosis between the 

 two veins, forming what is termed the arcus venosus jiiguli, and into this a number 

 of small branches from neighboring structures open. The horizontal portion of the 

 vein eventually pierces the posterior layer of the space to reach the external jugular. 



Variations. — The anterior jugular varies considerably in size, inversely to the external 

 jugular. Occasionally the two veins of opposite sides unite throughout the vertical portion of 

 their course to form a single stem, which passes down the median line of the neck and has con- 

 sequently been termed the v, mediana colli. 



The communicating branch from the facial vein, which passes downward along the anterior 

 border of the sterno-cleido-mastoid, is sometimes quite large, functioning as the direct continua- 

 tion of the facial, which may thus pour its blood mainly, if not entirely, into the anterior jugular. 

 Below, while the anterior jugular usually opens into the external jugular, yet it sometimes opens 

 directly into the subclavian, and occasionally it receives near its termination an external thoracic 

 vein, which ascends from the region of the mammary gland over the clavicle, posterior to the 

 attachment of the sterno-cleido-mastoid. 



The Subclavian Vein. 



The subclavian vein (v. subdavia) (Fig. 753) is the terminal portion of the venous 

 system of the upper extremity. It begins at the anterior border of the first rib, where 

 it is directly continuous with the axillary vein, and passes almost horizontally inward, 

 anterior to the scalenus anticus muscle and behind the clavicle, to the junction 

 of that bone with the sternum, where it unites with the internal jugular to form the 

 innominate vein. Its course is very similar to that of the subclavian artery, but it 

 is more horizontal and somewhat anterior to the artery, from which it is separated 

 by the scalenus anticus. 



It is provided with a pair of valves at its junction with the internal jugular and with 

 another pair at its junction with the axillary vein. In the first portion of its course it 

 is in relation anteriorly with the subclavius muscle, and its anterior wall is united to 



