<P> It is covered, in front, by the skin, the superficial fascia, the Platysma, the supraclavicular nerves, and the deep cervical fascia . The external jugular vein crosses its medial part and receives the transverse scapular, transverse cervical, and anterior jugular veins, which frequently form a plexus in front of the artery . Behind the veins, the nerve to the Subclavius descends in front of the artery . The terminal part of the artery lies behind the clavicle and the Subclavius and is crossed by the transverse scapular vessels . The subclavian vein is in front of and at a slightly lower level than the artery . Behind, it lies on the lowest trunk of the brachial plexus, which intervenes between it and the Scalenus medius . Above and to its lateral side are the upper trunks of the brachial plexus and the Omohyoideus . Below, it rests on the upper surface of the first rib . </P> <Table> <Tr> <Th> Part </Th> <Th> Branches </Th> <Th> Course </Th> </Tr> <Tr> <Td> First part <P> From its origin to the medial border of scalenus anterior </P> </Td> <Td> Vertebral artery </Td> <Td> Runs cranially in the transverse foramina of the cervical vertebrae, joins the vertebral artery on the contralateral side, forming the basilar artery and joins the circle of Willis . </Td> </Tr> <Tr> <Td> Internal thoracic artery </Td> <Td> Runs caudally behind the ribs, giving off anterior intercostal branches, perforating vessels to the breast and terminating in the superior epigastric artery and the musculophrenic artery </Td> </Tr> <Tr> <Td> Thyrocervical trunk </Td> <Td> Very short . Divides into inferior thyroid artery, suprascapular artery and transverse cervical artery (also called cervicodorsal trunk) </Td> </Tr> <Tr> <Td> Second part <P> Lying behind scalenus anterior </P> </Td> <Td> Costocervical trunk </Td> <Td> Splits into superior intercostal artery and deep cervical artery . </Td> </Tr> <Tr> <Td> Third part <P> Between the lateral border of scalenus anterior and the outer border of the first rib </P> </Td> <Td> Dorsal scapular artery </Td> <Td> From either second or third part . Passes backwards to supply levator scapulae and rhomboids . </Td> </Tr> </Table> <Tr> <Th> Part </Th> <Th> Branches </Th> <Th> Course </Th> </Tr> <Tr> <Td> First part <P> From its origin to the medial border of scalenus anterior </P> </Td> <Td> Vertebral artery </Td> <Td> Runs cranially in the transverse foramina of the cervical vertebrae, joins the vertebral artery on the contralateral side, forming the basilar artery and joins the circle of Willis . </Td> </Tr>

Where does the subclavian vein supply blood to