The: Thorax. 173 



sympathetic nerves, cannot be dissected in the order given below, but 

 must be separated from one another and identified as they appear. 



(a) The arch of the aorta (arcus aortae). Beginning at the base 

 of the heart, the aorta passes at first forward, and then 

 describing a curve, in the course of which it lies slightly to 

 left of the median plane, turns backward along the ventral 

 surfaces of the bodies of the thoracic vertebrae. With the 

 exception of the coronary arteries (p. 176), the first branches 

 are the large paired vessels arising from the anterior wall. 

 They comprise the common carotid and subclavian arteries. 

 On the right side the carotid and subclavian arise from a 

 short common trunk, the innominate artery (a. anonyma). 

 The left common carotid arises immediately to the left of this 

 vessel or from its base. 

 The branches of the common carotid artery have already been 

 traced, with the exception of the intra-cranial portion of the 

 internal carotid (p. 190). 

 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 

 is replaced by 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 seventh cerx'ical vertebra, 

 and traversing the canal formed by this and the correspond- 

 ing foramina of the remaining cervical vertebrae, reaches 

 the interior of the cranial cavity. Its union on the ventral 

 surface of the medulla oblongata with its fellow of the 

 opposite side to form the basilar artery will be seen at a later 

 stage (p. 190). 



(2) The superficial cervical artery (a. cervicalis superficialis) — 

 divided in a previous dissection (p. 135) — is a small vessel 

 which passes forward and outward beneath the insertions 

 of the cleidomastoideus, basioclavicularis 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. 136), 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 sup- 

 plies the serratus anterior and the rhomboidei. 



