The Thorax. 257 



(i) The vertebral artery (a. vertebralis). This vessel passes 

 into the costotransverse foramen of the sixth cervical verte- 

 bra, and traversing the canal formed by this and the corres- 

 ponding 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. 278). 



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

 — divided in a previous dissection (p. 206) — is a small 

 vessel which passes forward and outward beneath the in- 

 sertions 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. 207), 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 a. intercostalis suprema passes backward to the 

 internal surface of the thoracic wall, giving off the first chree 

 (or four) intercostal arteries in the intercostal spaces, and 

 also small branches to the oesophagus and trachea. 



(5) The internal mammary artery (a. mammaria interna), 

 the first portion of which has been removed with the ventral 

 wall of the thorax, passes backward to the ventral abdominal 

 wall as the superior epigastric artery (a. epigastrica 

 superior) anastomosing with the inferior epigastric (p. 203). 



(b) The superior caval vein (v. cava superior) is formed at the 

 base of the neck by the union of the internal and external 

 jugular veins, the latter vessel receiving at this point the 

 subclavian vein (v. subclavia). The right superior caval 



