Chap, ix.] THE NECK. 139 



The side of the neck. Muscles. The stemo- 

 mastoid muscle, especially in thin subjects and when 

 thrown into action, is a prominent feature in the 

 neck. The anterior border of the muscle is very 

 distinct. The posterior border is less prominent, 

 especially at its upper part. A communicating branch 

 from the facial vein generally runs along the anterior 

 border of the muscle to meet the anterior jugular vein 

 at the lower part of the neck. The interval between 

 the sternal and clavicular parts of the muscle is 

 generally well marked. If a needle be thrust through 

 this interval, quite close to the clavicle, it would just 

 touch the bifurcation of the innominate artery on the 

 right side and would pierce the carotid vessel on the 

 left. The posterior belly of the digastric muscle 

 corresponds to a line drawn from the mastoid process 

 to the anterior part of the hyoid bone. The anterior 

 belly of the omo-hyoid follows an oblique line drawn 

 downwards from the fore-part of the hyoid bone, so as 

 to cross the line of the carotid artery opposite the 

 cricoid cartilage. The posterior belly can be made 

 out in thin necks, especially when in action, running 

 nearly parallel with and just above the clavicle. 

 Although not taking quite the same direction, yet the 

 posterior borders of the sterno-mastoid and anterior 

 scalene muscles practically correspond to one another. 



Vessels. The common carotid artery is represented 

 by a line drawn from the stemo-clavicular joint to a 

 point midway between the angle of the jaw and the 

 mastoid process. The vessel bifurcates at the upper 

 border of the thyroid cartilage. The omo-hyoid 

 crosses it opposite the cricoid cartilage, and at about 

 the same level the art-ery is crossed by the middle 

 thyroid vein. The line of the internal jugular vein is 

 just external to that for the main artery. The 

 superior thyroid artery comes off just below the great 

 cornu of the hyoid bone, and curves forwards and 



