THE NECK. 139 



region of the neck in some cases it is necessary to divide this vein; in others one 

 may be able to avoid it, at all events it should be recognized before the incision is 

 made. Behind the angle of the jaw there is usually a branch communicating with 

 the facial, lingual, or internal jugular vein, and just above its lower extremity it is 

 enlarged, forming the part called the sinus. For these reasons, if the vein is cut low 

 down near the clavicle or high up near the angle of the jaw bleeding is liable to be 

 free. The valves are not competent to prevent the reflux of blood and it therefore 

 drains the large internal jugular above and the subclavian below. The attachment 

 of the vein to the deep fascia, as it pierces it above the clavicle, tends to keep its 

 lumen open when the vein is divided and favors the entrance of air into the circula- 

 tion. The size of the veins in the posterior triangle varies according to those in the 

 anterior. If the anterior and external jugulars are large the posterior and internal 

 jugulars are apt to be small. 



Arteries. The arteries in the posterior cervical triangle are the subclavian, the 

 transverse cervical, and sometimes the suprascapular when it runs above the clavicle 

 instead of behind it. The line of the subclavian is from the sternoclavicular joint to 

 the middle of the clavicle. It rises about 1.25 cm. (^ in.) above the clavicle. The 

 clavicular origin of the sternomastoid muscle covers the inner third of the clavicle so that 

 the subclavian artery is only visible in the posterior cervical triangle from the outer 

 edge of this muscle to the middle of the clavicle. Both the suprascapular and 

 transverse cervical arteries are given off from the thyroid axis, which arises from the 

 third portion of the subclavian just internal to the scalenus anticus muscle. Therefore 

 at their origin they are both considerably above the level of the clavicle, but as they 

 proceed outward they incline downward, and on leaving the outer edge of the sterno- 

 mastoid muscle the suprascapular is usually behind the clavicle while the transverse 

 cervical runs parallel to it and a short distance (i cm.) above it, where it can be 

 felt pulsating. 



The posterior belly of the omohyoid muscle can be represented by a line drawn 

 from the anterior edge of the sternomastoid muscle opposite the cricoid cartilage, 

 obliquely down and out to the junction of the middle and outer thirds of the clavicle. 

 It is superficial to the transverse cervical artery and at its inner end is above it. 

 These arteries and their accompanying veins will be encountered in operating in 

 these regions for the removal of lymphatic nodes. 



Nerves. -The nerves in the posterior cervical triangle are the spinal accessory, 

 branches of the cervical plexus, and the brachial pie xiis. The position of the spinal 

 accessory is important because it is frequently encountered in operations for the 

 removal of enlarged lymphatic nodes. It enters the under surface of the sternomastoid 

 muscle from 3 to 5 cm. below the tip of the mastoid process and emerges at the pos- 

 terior edge about its middle or a little above. It is about at this point that the 

 external jugular vein reaches the posterior border of the sternomastoid, and the cervical 

 plexus, formed by the anterior divisions of the four upper cervical nerves, reaches 

 the surface. From this point also the occipitalis minor runs upward along the posterior 

 edge of the sternomastoid and the auricularis magnus runs upward over the sterno- 

 mastoid direct to the external ear. The superficial cervical runs directly across the 

 muscle towards the median line and the descending branches the sternal, clavicular, 

 and acromial pass down beneath the deep cervical fascia to perforate it just above the 

 clavicle and become cutaneous. Care should be taken not to mistake them for the 

 spinal accessory. Still deeper are the cords of the brachial plexus. These cords, 

 sometimes two, at others three in number, are beneath the deep fascia and lie above 

 the subclavian artery. They can be felt and in a thin person, if the head is turned to 

 the opposite side, the prominence which they form under the skin can even be seen. 



Lymphatics. The lymphatics of the posterior cervical triangle are numerous 

 and being often enlarged are frequently operated on. They lie along both the outer 

 side of the internal jugular vein and under the posterior edge of the sternomastoid 

 muscle, which they follow clear up to the base of the skull. They also follow the edge 

 of the trapezius muscle and lie in the space between it and the sternomastoid; they 

 extend downward under the clavicle and become continuous with the axillary 

 lymphatics. The right and left lymphatic ducts empty into the venous system at 

 the junction of the innominate and internal jugular veins. That on the left side is 



