that they don't pass the needle too far and start
rupturing these structures. Now let's move
on to the posterior compartment of the arm.
These muscles that lie behind the humerus and
the median lateral intermuscular septae. What
we have is triceps brachii. This muscles has
got three heads, a long head, a lateral head
and a medial head which we've seen some of before.
We have mentioned the long head when we covered
various spaces. We can see the long head here
is passing from the infraglenoid tubercle
of the glenoid cavity. A long head of biceps
went to the supraglenoid tubercle. Well the long
head of triceps is coming from the infraglenoid
tubercle. It then unites to form this common
tendon where the medial head and lateral head
converge and all three attached on the olecranon.
We've also got a small muscle here which is
known as anconeus coming from the lateral
epicondyle of the humerus towards the olecranon
here, anconeus. But I won't really mention that. So
if we look at the detail we have got triceps
brachii, we have got the long head coming from
the infraglenoid tubercle. We have got a lateral
head and medial head. The lateral head is
coming from posterior, the humerus is
coming from superior to the radial groove.
So if we look here, the lateral head, this is the
radial groove running down here. Superior to
the radial groove we have the lateral head.
Inferior to the radial groove we have the
medial head. So here we can see superior to
the radial groove the lateral head, inferior
to the radial groove the medial head, separated
by the radial groove here. We will later on
see the important blood vessel, and nerves
run along here. All of these three muscles
converge onto the olecranon. They are supplied
by the radial nerve and they are important
in extending the elbow joint. So there the
antagonist of brachialis and biceps. The long
head because it crosses the glenohumeral joint
also serves to extend the shoulder joint.
I said I have mention it just briefly about
we've got anconeus running from the lateral epicondyle
of humerus to olecranon also supplied by
the radial nerve and this really supports
triceps in extending the elbow joint.
So here we've got two dissections. Two cartoons showing
dissections of the posterior aspect.
Here we have got the slightly more lateral of view.
We have got deltoid still intact and we can
see coming from this bottom inferior border
of deltoid we have got the various heads long
head, lateral head and the medial head down
here of triceps running towards the olecranon.
When here when deltoid has been exposed we moved deltoid,
we can say that these muscles are running
down towards the olecranon. We can see the
olecranon here. We can see the radial groove
here. We can see we have got the lateral head
of triceps here and also here. What we have
done is we have cut through the lateral head
of triceps to expose this medial head coming
from inferior to the radial groove. We have
still got the long head up here. We can see
it forming the quadrangular space here. We
have got the long head. We have got the lateral
head which has been cut is the other side
of the lateral head and we have got the
medial head. These all converging with anconeus on
to the olecranon. So the proximal attachments
of the triceps are shielded by deltoid. But removal
of deltoid can highlight their attachments
as we can see in this image down at the bottom.
We can see the lateral intermuscular septum.
The lateral intermuscular septum here separating
the anterior from the posterior compartments.
And we can also in this diagram here remind ourselves
of those three spaces on the posterior wall
of the axilla. So the quadrangular space we
can see here, the triangular space we can
see here and the triangular slit or the
triangular interval we can see here.
We can also in relation to the radial groove see the origin
of the medial and lateral heads of triceps.