Now that we looked at the anterior triangle of
the neck, we're going to look on the other
side of the sternocleidomastoid to find the
So the boundaries of the posterior triangle
are the posterior edge of the
sternocleidomastoid, the trapezius muscle,
and the middle third or so of the clavicle.
The posterior triangle has what we consider a
floor, which are the muscles deep to this
area, which are the splenius, capitis,
levator scapulae, and the three scalene
muscles posterior, middle, and anterior.
We can divide the posterior triangle a little
bit more, but really only into two smaller
ones. We can divide it on either side of the
inferior belly of the omohyoid, whereas
inferior to that we will have the
omoclavicular or subclavian triangle, and
superior to it would be the occipital
Let's look at some of the contents of the
posterior triangle, starting with the external
External refers to its location, external to
And here we see that external jugular vein
coming down into the subclavian vein where it
drains. We also see posterior to that the
And if we fade out the sternocleidomastoid,
we see the accessory nerve, which is what
innervates the sternocleidomastoid and
We also see this very important plexus of
nerves called the cervical plexus, as well as
a collection of nerves that are going to
supply the upper limb called the brachial
plexus. So let's look again at that external
In terms of venous drainage of the face, the
retromandibular vein does the majority of the
work and it has an anterior and posterior
In this case, we're going to look at that
posterior branch that merges with the
posterior auricular vein coming from behind
the ear to actually form the external jugular
vein, which will in turn drain into the
Now let's take a look at the subclavian
Here we see the subclavian artery arising
from the brachiocephalic trunk on the right
side. On the left, the subclavian artery
arises directly from the aortic arch owing to
the asymmetry of this area.
After the subclavian artery passes the outer
border of the first rib, it's going to change
name to the axillary artery.
And eventually, that will even change its
name to the brachial artery as it enters the
If we zoom in a little bit more.
Here we see this muscle called the anterior
And this is the muscle behind which the
subclavian artery is going to pass anterior to
the scalene muscles where we would find the
The subclavian artery here can be divided
into the prescalene part or the portion
proximal to the anterior scalene.
The retroscalene part, the part that's
sitting just behind it.
And then the short postscalene part just
before it turns into the axillary artery.
In terms of the prescalene part, we have the
vertebral artery and that's a very important
artery in this area because this is the
artery that's going through the transverse
foramina of the cervical vertebra on its way
up into the brain to form a very important
anastomosis in the circle of Willis.
At about this same area but traveling
inferiorly would be the internal thoracic
artery, very important artery for the thorax.
We also have the thyrocervical trunk, which is
a short trunk that branches into the
suprascapular artery, the transverse cervical
artery, and the inferior thyroid artery.
The superior will be a branch of the external
In terms of the retroscalene part, we have
the costocervical trunk, which is going to
give rise to the deep cervical artery, the
supreme intercostal artery, which is just the
uppermost intercostal artery, and the dorsal
Now let's take a look at the nerves in this
They come from a plexus called the cervical
Here we see the cervical spinal roots C1, C2,
C3, and C4.
Several cutaneous nerves come off of this
area, including the lesser occipital, great
auricular, transverse cervical, and the
We also see C1, C2, and C3 forming this loop
called the ansa cervicalis.
And this is going to provide motor supply to
the infrahyoid muscles, with the exception of
thyrohyoid, which is only receiving motor
innervation from C1.
If we throw in C5 as well, we see the origins
of the phrenic nerve, which is composed of
roots from C3, C4, and C5 before it goes all
the way down to supply the diaphragm.
So here are those cutaneous branches.
We see the lesser occipital going in the area
of the occipital bone, the great auricular in
the general area of the ear, the transverse
cervical and supraclavicular nerves.
And as you can see, they're all mostly in the
posterior area of the head and neck.
And that's because the anterior portion of
the head gets its cutaneous innervation from
the trigeminal nerve.