Now, we’ll move on and take a look at the subclavian artery. There are four branches
associated with the subclavian artery. The first and a very significant branch is the
vertebral artery that we see in through here. It will help supply blood to the brain along with
the internal carotids that we mentioned earlier. Second branch of the subclavian artery is a trunk.
This is referred to as the thyrocervical trunk. We see it issuing from the right subclavian in this
area. The third branch is the costocervical trunk. This is a smaller branch that we see in
through here. As the name implies, this will help to supply the ribs, the upper two ribs.
Then it has an outstanding course to help supply cervical-related structures. Then your fourth
and final branch is a descending branch. This is your internal thoracic artery. It’s descending
along the lateral margin of the sternum. Of the branches of the subclavian artery, the vertebral
artery is important in that it supplies, with the assistance of the internal carotids, it supplies
the brain with blood. The vertebral artery has a curious course to help to supply the brain
with blood and that it will pass through the transverse foramina of the cervical vertebrae.
There are variations on how it does so. The most common is for the vertebral artery that we see
here to pass through the transverse foramen of C6. It will then ascend through all the other
sequential transverse foramina until it passes through the one associated with C1.
It then will curve medially and then loop upwards through the foramen magnum to help
supply the brain with blood. In 5% of the cases, the vertebral artery will skip the transverse
foramina of C7 and C6 and enter at the level of C5. In 2% of the cases, it will enter either at C7
and then pass through all the sequential transverse foramina or with 2% of the other cases,
it will pass through at the level of C4. Then the last and final variation here is the least
frequent variation. This occurs about 1% of the time. Here, the vertebral artery will enter
at the transverse foramen associated with the third cervical vertebra and then pass through
C2 and then C1 to enter. This is called the help supply cerebral circulation.