78 DISSECTION OF THE NECK. 



artery, and coursing downwards beneath the clavicle, subclavius T and the 

 right innominate vein, enters the thorax between the first rib and the bag 

 of the pleura. As the artery disappears in the chest, it is crossed (super- 

 ficially) by the phrenic nerve. The vessel is distributed to the walls of 

 the chest and abdomen ; and its anatomy will be given with the dissection 

 of those parts. 



Thyroid axis. This is a short thick trunk (fig. 16) which arises from 

 the front of the artery near the anterior scalenus muscle, and soon divides 

 into three branches one to the thyroid body, and two to the scapula. 



The suprascapular branch courses outwards across the lower part of the 

 neck, behind the clavicle and subclavius muscle, to the superior costa of 

 the scapula, and entering the supraspinal fossa is distributed on the dorsum 

 of that bone. The connections of this artery are more fully seen in the 

 dissection of the Back. 



The transverse cervical branch, usually larger than the preceding, takes 

 a similar direction, though higher in the neck, and ends beneath the bor- 

 der of the trapezius muscle in the superficial cervical and posterior scapular 

 arteries. (" DISSECTION OF THE BACK.") In its course outwards through 

 the space containing the third part of the subclavian artery, this branch 

 crosses the anterior scalenus, the phrenic nerve, and the brachial plexus. 

 Some small offsets are supplied by it to the posterior triangular space of 

 the neck. 



Though the transverse cervical artery supplies ordinarily the posterior 

 scapular branch, there are many bodies in which it is too small to give 

 origin to so large an offset. In such instances the diminished artery ends 

 in the trapezius muscle ; whilst the posterior scapular branch arises sepa- 

 rately from the third, or even the second part of the subclavian artery 

 (fig. 16). 



The inferior thyroid branch is the largest offset of the thyroid axis. 

 Directed inwards with a flexuous course to the thyroid body, the branch 

 passes beneath the common carotid artery and the accompanying vein and 

 nerves, and in front of the longus colli muscle and the recurrent nerve. 

 At the lower part of the thyroid body it divides into branches which ramify 

 in the under surface, and communicate with the superior thyroid, and its 

 fellow, forming a very free anastomosis between those vessels. 



Near the larynx a laryngeal branch is distributed to that tube, and other 

 offsets are furnished to the trachea. 



The ascending cervical branch of the thyroid is directed upwards be- 

 tween the scalenus and rectus capitis anticus major, and ends in branches 

 to those muscles and the posterior triangle of the neck. Some small spinal 

 offsets are conveyed along the spinal nerves to the cord and its membranes. 



The veins corresponding with the branches of the thyroid axis have the 

 following destination : those with the suprascapular and transverse cervical 

 arteries open into the external jugular vein. But the inferior thyroid vein 

 begins in the thyroid body, and descends in front of the trachea, beneath 

 the muscles covering this tube, to the innominate vein. 



The superior intercostal artery arises from the posterior part of the sub- 

 clavian, and bends downwards over the neck of the first rib : its distribu- 

 tion to the first two intercostal spaces will be seen in the thorax. 



Arising in common with this branch is the deep cervical artery (art. pro- 

 funda cervicis). Analogous to the dorsal branch of an intercostal artery 

 (Quain), it passes backwards between the transverse process of the last 

 cervical vertebra and the first rib, lying internal to or beneath the two 



