The Vascular System 219 



The left subclavian artery, sc.s., although it has a 

 different origin, has the same branches as described 

 in connection with the right subclavian. The 

 exact order in which the first of these (the thyroid, 

 th; the internal mammary, im'; the coUateralis 

 colli, cc; the pleural, plu; and the vertebral, v') 

 are given off is, as might be expected, subject to 

 some variation. 



The coUateralis colli, cc (following Bronn's 

 nomenclature), whose origin was noted above, 

 will now be discussed ; since the two are alike only 

 one need be described. After leaving the sub- 

 clavian, it passes cephalad, at the side of the trachea 

 and oesophagus, in company with the internal 

 jugular vein, so that in this part of its course 

 it would seem to be the internal carotid artery. It 

 gives numerous small twigs to the trachea and 

 oesophagus, oe. In the region of the posterior part 

 of the huge jaw muscle it is connected directly, x, 

 with the adjacent branch, cm (called by Bronn the 

 common carotid) of the primary carotid, and 

 indirectly, x',with a complicated group of branches 

 from the common carotid. Cephalad to the 

 connective x^ which extends dorsad and is hence 

 foreshortened in the figure, the coUateralis colli 

 gives off a small vessel, y (too large in Fig. 62) , to the 

 shoulder and skin; it then sends a fairly large 

 branch, jm, into the large jaw muscle, close to 

 which it now lies. Next a small branch, Ig, is sent 

 to the larynx. Continuing cephalad and laterad 



