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THE THORAX. 257 
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). 
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. 
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 rhomboidel. 
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. 
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). 
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 
