Flexor digitorum profundus is a deep muscle of the forearm, all the other choices are superficial muscles of the forearm.

The rhomboid major and rhomboid minor muscles are responsible for retraction and elevation of the scapula. Both the rhomboid major and minor are innervated by the dorsal scapular nerve. The levator scapulae also helps elevate the scapula. The important distinction is that the rhomboids both originate from the vertebrae and insert on the medial border of the scapula. It is this pathway that allows for both elevation and retraction.

The trapezius helps elevate the scapula and raise the upper limb above the head, but is not associated with retraction of the scapula. The deltoid muscle is responsible for abduction of the arm beyond the initial fifteen degrees accomplished by the supraspinatus muscle. The latissimus dorsi extends, adducts, and medially rotates the arm.

If a muscle is split into multiple heads, there will usually be some indication in the name of the muscle. There are two answer choices which fit this category: biceps brachii and triceps brachii. "Bi" means two while "tri" means three, which means the correct answer is the biceps brachii. The triceps brachii has a long head, a lateral head, and a posterior head.

The upper and lower trapezius function to upwardly rotate the scapula, as does the serratus anterior. Although the rhomboids (major and minor) can elevate the scapula, they are downward scapular rotators. Additionally, although the middle trapezius attaches to the scapula, it does not contribute to scapular upward rotation, due to the transverse orientation of its fibers.

The coracobrachialis originates on the coracoid process, and inserts to the medial shaft of the humerus. The cheat in this question is to look at the base word - coracobrachialis.

In order to cause flexion or extension of a joint, a muscle must originate on one side of the joint and insert on the other. In other words, the muscle body must cross the joint in order to affect it.

The biceps brachii, brachialis, corocobrachialis, and brachioradialis originate from the scapula or humerus and insert on the radius or ulna. Each of these muscles thus crosses the elbow. In contrast, the flexor carpi radialis originates on the radius and inserts on the second metacarpal. When contracted, the flexor carpi radialis causes flexion of the hand at the wrist, but does not affect the position of the forearm.

A muscle that would only be responsible for the pinky finger would be a small one. In addition, extensor muscles of the hand are located in the posterior compartment, whereas flexors are located anteriorly. Of the following choices, the smallest muscle is the extensor digits minimi, which is also located posteriorly. It aids in abduction of the 5th digit as well.

Three muscles attach to the coracoid process in the upper extremity. The pectoralis minor, coracobrachialis, and the short head of biceps brachii all attach to the coracoid process. The pectoralis major does not attach to the coracoid process, but it attaches to the humerus (deltoid also attaches to the humerus).

The musculocutaneous nerve (C5, C6, C7) runs the length of corachobrachialis and brachialis.

The biceps brachii is the only muscle of the answer choices that flexes the elbow but also is a strong supinator of the forearm. It inserts on the radius, which accounts for its supinating action. Brachialis inserts onto the ulna, and thus, has no supinating action.

The only muscle listed that receives its primary blood supply from the brachial artery is the biceps (more specifically known as the biceps brachii).

The other muscles listed receive their blood supply as follows:

Deltoid: Thoracoacromial artery, and anterior and posterior circumflex humeral arteries

Subscapularis: Subscapular artery

Teres major: Subscapular and circumflex scapular arteries

Teres minor: Posterior circumflex humeral artery and circumflex scapular artery