THE THORAX 325 



carotid arises immediately to the left of this vessel or from 

 its base. The left subclavian arises some distance farther 

 out along the arch. The subclavian artery (a. subclavia) 

 is the first portion of the artery of the anterior limb. It 

 passes from its point of origin laterad to the anterior margin 

 of the first rib, where it becomes the axillary artery. Near 

 its point of origin it gives off several branches, the relations 

 of which are subject to considerable variation. They 

 include: 



(1) The vertebral artery (a. vertebralis). This vessel 

 passes into the costotransverse foramen of the sixth 

 cervical vertebra, and, traversing the canal formed by 

 this and the corresponding foramina of the vertebrae 

 anterior to it, reaches the interior of the cranial cavity. 

 Its union on the ventral surface of the medulla oblon- 

 gata with its fellow of the opposite side to form the 

 basilar artery will be seen at a later stage (p. 360). 



(2) The superficial cervical artery (a. cervicalis super- 

 ficialis) — divided in a previous dissection (p. 258) — is 

 a small vessel which passes forward and outward be- 

 neath the insertions of the cleidomastoideus, basio- 

 clavicularis, and levator scapulae major muscles, 

 ramifying extensively in the fat mass of the side of 

 the neck under cover of the superior portion of the 

 trapezius. Its ascending cervical branch lies on the 

 lateral side of the external jugular vein. 



(3) The transverse artery of the neck (a. transversa colli), 

 also divided in a previous dissection (p. 260), passes 

 laterad around the neck of the first rib to the wall of 

 the thorax. It passes through the loop formed by the 

 eighth cervical and first thoracic spinal nerves. It 

 runs dorsad, first on the medial side of the scalenus 

 anterior, then on the medial side of the cervical portion 

 of the serratus anterior. A strong branch passes to the 

 inferior angle of the scapula. The artery supplies the 

 serratus anterior and the rhomboidei. 



(4) The highest intercostal artery (a. intercostalis suprema) 



