The vertebral artery is the first branch of the subclavian artery as it enters the root of the neck (Fig. 8.191). A large branch, arising from the first part of the subclavian artery medial to the anterior scalene muscle, it ascends and enters the foramen in the transverse process of vertebra CVI. Continuing to pass superiorly, the vertebral artery passes through the foramina of vertebrae CV to CI. At the superior border of vertebra CI, the artery turns medially and crosses the posterior arch of vertebra CI. From here it passes through the foramen magnum to enter the posterior cranial fossa.
The second branch of the subclavian artery is the thyrocervical trunk (Fig. 8.191). It arises from the first part of the subclavian artery medial to the anterior scalene muscle, and divides into three branches—the inferior thyroid, the transverse cervical, and the suprascapular arteries.
Inferior thyroid artery. The inferior thyroid artery (Fig. 8.191) is the superior continuation of the thyrocervical trunk. It ascends, anterior to the anterior scalene muscle, and eventually turns medially, crossing posterior to the carotid sheath and its contents and anterior to the vertebral artery. Reaching the posterior surface of the thyroid gland it supplies the thyroid gland.
When the inferior thyroid artery turns medially, it gives off an important branch (the ascending cervical artery), which continues to ascend on the anterior surface of the prevertebral muscles, supplying these muscles and sending branches to the spinal cord.
Transverse cervical artery. The middle branch of the thyrocervical trunk is the transverse cervical artery (Fig. 8.191). This branch passes laterally, across the anterior surface of the anterior scalene muscle and the phrenic nerve, and enters and crosses the base of the posterior triangle of the neck. It continues to the deep surface of the trapezius muscle, where it divides into superficial and deep branches:
The superficial branch continues on the deep surface of the trapezius muscle.
The deep branch continues on the deep surface of the rhomboid muscles near the medial border of the scapula.
Suprascapular artery. The lowest branch of the thyrocervical trunk is the suprascapular artery (Fig. 8.191). This branch passes laterally, crossing anterior to the anterior scalene muscle, the phrenic nerve, the third part of the subclavian artery, and the trunks of the brachial plexus. At the superior border of the scapula, it crosses over the superior transverse scapular ligament and enters the supraspinatus fossa.
The third branch of the subclavian artery is the internal thoracic artery (Fig. 8.191). This artery branches from the inferior edge of the subclavian artery and descends.
It passes posterior to the clavicle and the large veins in the region and anterior to the pleural cavity. It enters the thoracic cavity posterior to the ribs and anterior to the transversus thoracis muscle and continues to descend giving off numerous branches.
The final branch of the subclavian artery in the root of the neck is the costocervical trunk (Fig. 8.191). It arises in a slightly different position, depending on the side:
On the left, it arises from the first part of the subclavian artery, just medial to the anterior scalene muscle.
On the right, it arises from the second part of the subclavian artery.
On both sides, the costocervical trunk ascends and passes posteriorly over the dome of the pleural cavity and continues in a posterior direction behind the anterior scalene muscle. Eventually it divides into two branches—the deep cervical and the supreme intercostal arteries:
The deep cervical artery ascends in the back of the neck and anastomoses with the descending branch of the occipital artery.