|Derivation||Brachia, the upper arm.|
|Origin||Anterior surface of humerus.|
|Insertion||Anterior surface on the head of the ulna.|
|Action||Bends the arm at the elbow.|
Brachialis underlies the lower portion of the biceps and shares its function of bending the elbow. From the front, it pokes out on either side of the biceps. (In this respect it is interesting to compare it to the soleus muscle on the leg.)
Its origin is directly below the insertion of the deltoid. Their fibers blend, but there is a notable plane break between them. The deltoid seems to point downward at brachialis here.
It disappears between the biceps tendon and brachioradialis on the way to its insertion on the ulna.
On the lateral side, brachialis is a prominent, sometimes distinct form between the biceps and triceps below the deltoid.
On the medial side, it lies under of layer of flesh, but can be seen lending fullness to the arm immediately to the side of and below the biceps.