Figure 11-3
Cross section of the middle of the arm.

Move on to the arm and its structures. First locate the muscles of the anterior arm. The biceps brachii is the most superficial and obvious. It has two proximal attachments (two heads), and thus its name. Locate the short head of the biceps and the long head of the biceps. The short head actually appears longer, but runs to the coracoid process (confirm by locating pectoralis minor). The long head runs up and through the bicipital groove over the head of the humerus to the supraglenoid tubercle.

Now that you have found the short head of the biceps, the coracobrachialis should be easy to locate as it also attaches proximally to the coracoid process. The brachialis is the deepest of these muscles and only crosses the elbow. Motor innervation by the musculocutaneous nerve is readily apparent.

The posterior compartment of the arm houses only one muscle, the triceps brachii. As the name implies, this muscle has three heads. One of these heads, the long head of the triceps brachii, actually crosses the shoulder joint and inserts on the infraglenoid tubercle of the scapula. This head of the triceps has its primary affect on the shoulder joint. The lateral and medial heads of the triceps attach on the posterior body of the humerus proximally, and insert distally on the olecranon process of the ulna. The medial head is deep to the lateral head, and, if the proximal end of the lateral head has not been cut, is hard to see. If it has been cut, you should see the radial nerve and the profunda brachii artery running together distally between the lateral head and the medial head of the triceps.