vein, giving off branches to the internal intercostal muscles. Trace it posteriorly along the dorsal surface of the rectus abdominis muscle, to which it sends branches. Several branches perforate the intercostal muscles and supply the pectoral and rectus abdominis muscles. Find the right internal mammary artery. Its branches and course are substantially the same as for the left internal mammary.
The vertebral artery upon leaving the subclavian passes cephalad about half a centimeter and enters the vertebrarterial canal at the sixth cervical vertebra. This canal consists of the transverse foramina of the cervical vertebrae. Running forward through this canal, the artery sends off branches between the vertebrae. It traverses the transverse foramen of the atlas, gives off a branch through the large oval foramen on the dorsal side of this vertebra, passes through the atlantal foramen, and enters the cranial cavity by way of the foramen magnum.
Thyro-cervical trunk. It leaves the subclavian artery medial to the first rib and passes anterolaterally to a position dorsal to the proximal end of the clavicle, where it divides into several branches. These branches supply glands on the surface of the neck, and muscles of the neck region.
Costo-cervical trunk. This vessel leaves the subclavian artery at the same level as the internal mammary, courses laterally anterior to the first rib, then sends branches to the lateral muscles of the thorax and deeper muscles of the neck.
The axillary artery is the continuation of the subclavian lateral to the first rib. Its branches are as follows.
(1) Lateral thoracic artery. It proceeds caudally from the axillary artery along the medial surface of the cutaneous maximus muscle.
(2) Subscapular artery. It arises from the axillary artery and divides into branches which supply muscles in the upper arm and thorax.
