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.

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

The lateral and medial heads of the triceps brachii originate on the humerus and attach to the ulna. The long and short heads of the biceps brachii attach to the scapula at the supraglenoid tubercle and the coracoid process, respectively. The long head of the triceps brachii attaches to the scapula at the infraglenoid tubercle. The supraspinatus attaches to the scapula at the supraspinous fossa.

The insertions of the trapezius muscle are the superior spine of the scapula, posterior lateral one-third of the clavicle, and the acromion (spinotrapezius, clavotrapezius, and acromiotrapezius). The acromion is one origin for the deltoid, however, it's insertion is only the deltoid tuberosity of the humerus. All of the other answers are incorrect since their insertions are on the posterior medial border of the scapula.

The brachialis only produces motion across one joint; it flexes the elbow. The biceps brachii flex the shoulder and elbow and supinate the forearm. The triceps brachii extends both the shoulder and elbow. The extensor carpi radialis longus produces motion across the elbow and the wrist.

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 deltoid is innervated by the axillary nerve. Its function is to abduct, flex, and extend the humerus. The three major fibers have their origins on the lateral third of the clavicle, acromion, and the spine of the scapula. All three parts of the deltoid insert into the deltoid tuberosity on the lateral aspect of the humerus.

The supraspinatus and infraspinatus muscles are innervated by the suprascapular nerve. The triceps brachii are innervated by the radial nerve. The median nerve innervates various muscles of the forearm.

The correct answer is the 2nd metacarpal. We can come to this conclusion by looking at the name of the muscle. Because of the word radialis, we know that the muscle should should run along the radius and insert into one of the lateral metacarpals when in the anatomical position, leaving us with the answer choices: 1st and 2nd metacarpals. In addition, it is the 2nd over the 1st because any muscle dealing with the thumb will contain the word pollicus.

The humerus is located in the upper arm, meaning the muscle should also be located in the upper arm. This leaves us with the triceps brachii and biceps brachii as possible answer choices. The correct answer is the triceps brachii because it of its action as an extensor muscle.

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.