Upper Limbs Muscle Anatomy

In addition to the bones of the upper arm, forearm, and hand, the scapula and clavicle are also part of the upper limb.

The scapula and clavicle form the girdle of the upper limb. Thus, there are bones of the free upper limb and bones of the upper limb girdle.

This principle also applies to the muscles. There are muscles of the free upper limb, that is, the arm, forearm, and hand, and muscles of the upper limb girdle associated with the scapula and clavicle.

As you know, we present the basic aspects of the human body that are important to artists and useful for understanding drawing basics. Therefore, we will only tell you about the large superficial muscles that form the visible contours of the body.

Muscles of the Upper Limb Girdle

Deltoid

There are many misconceptions associated with this muscle. Many call it the “shoulder muscle” or “arm muscle.” In fact, the deltoid belongs to the muscles of the upper limb girdle.

This muscle forms the rounded contour of the shoulder, especially in a person with developed muscles. You’ve probably seen these round forms on the shoulders of comics superheroes. But despite this, the deltoid is not a muscle of the upper arm.

The deltoid muscle starts from the lateral third of the clavicle, acromion, and spine of the scapula. As you can see, the deltoid muscle occupies a fairly large area.

This muscle attaches to the deltoid tuberosity of the humerus. By contracting, the deltoid can move the arm away from the body. The deltoid muscle is located directly under the skin, so it is very important in plastic anatomy.

Infraspinatus Muscle

As you remember, the posterior surface of the scapula is divided into two large areas – the supraspinous and infraspinous fossae.

The boundary between these fossae is a bony protrusion called the spine of the scapula. Both fossae are filled by the corresponding muscles. The infraspinatus muscle is relatively large, and part of it contributes to the visible form of the back of the shoulder.

The infraspinatus muscle occupies the infraspinous fossa on the posterior surface of the scapula. Part of it is covered by the deltoid muscle. The infraspinatus begins from the infraspinous fossa and attaches to the greater tubercle of the humerus. By the way, many people mistakenly consider this muscle to be one of the back muscles; this is a common misconception.

Muscles of the Upper Arm

The muscles of the upper arm are classified into anterior and posterior groups. The anterior group includes the biceps brachii, brachialis, and coracobrachialis muscles. The posterior group is formed mainly by the large triceps brachii muscle.

Biceps

Probably, many people know where this muscle is located because exercises for the biceps are among the most common and familiar in many gyms.

The biceps occupies the anterior surface of the upper arm. In athletic people, the biceps forms a prominent, rounded contour, which is especially noticeable when the elbow is bent. One of the main functions of this muscle is to flex the forearm at the elbow joint.

The biceps has two heads. The long head starts from the supraglenoid tubercle of the scapula. The short head starts from the apex of the coracoid process of the scapula. Both heads converge into a large muscle belly, which passes across the elbow joint and attaches to the tuberosity of the radius.

Triceps

The contour of the back of the upper arm, where it is not covered by the deltoid, is formed largely by the powerful triceps muscle. The triceps has three heads – long, lateral, and medial. The medial head lies deeper than the other two and is therefore less visible on the surface.

Only the long head of the triceps attaches to the scapula, beginning from the infraglenoid tubercle. The lateral and medial heads begin from the posterior surface of the humerus. All three heads connect to form a single tendon that attaches to the olecranon of the ulna. The main function of the triceps is to extend the forearm at the elbow joint. The long head also helps extend the arm at the shoulder joint.

Muscles of the Forearm

This is a very numerous group of large, developed muscles. The forearm muscles act on the highly mobile joints of the wrist, hand, and fingers. On the front and back of the forearm, the muscles are arranged in several layers. We will not consider the deep muscles, but we will study the largest superficial muscles that form the contours of the upper limb.

Front Surface

Brachioradialis Muscle

This muscle occupies the lateral side of the forearm when the arm is in the anatomical position. As you remember, the radius corresponds to the thumb side, and the ulna corresponds to the little finger side. The brachioradialis muscle is also located on the side of the thumb. This muscle is especially developed in gymnasts and climbers.

Spider-Man also has very pronounced forearm muscles because he constantly hangs from webs and climbs.

The brachioradialis muscle starts from the humerus above the lateral epicondyle and attaches near the lower end of the radius. The main function of the brachioradialis is to flex the forearm at the elbow joint.

Pronator Teres Muscle

You can easily find the pronator teres using the previous muscle as a landmark. The brachioradialis and pronator teres form the sides of a V-shaped area near the elbow. In people with developed muscles, the pronator teres can also be clearly visible because of its superficial position.

The pronator teres starts from the medial epicondyle of the humerus and the coronoid process of the ulna. This muscle attaches to the lateral surface of the radius. The pronator teres pronates the forearm and also assists with flexion at the elbow.

Flexor Carpi Radialis Muscle

We continue to study the superficial muscles of the forearm. The flexor carpi radialis lies next to the pronator teres. It is a long muscle that extends from the medial epicondyle of the humerus toward the bases of the second and third metacarpal bones.

The flexor carpi radialis has a long tendon that becomes visible under the skin near the wrist. The main function of this muscle is to flex the hand at the wrist.

Palmaris Longus Muscle

If we move a little more medially, we see another muscle with a very long tendon. It extends from the medial epicondyle of the humerus to the hand, where its tendon blends with the palmar aponeurosis – a wide connective tissue layer located under the skin of the palm.

The tendon of this muscle is located very superficially, so it can protrude clearly under the skin when the wrist is flexed. The function of this muscle is to flex the hand at the wrist.

Back Surface

Extensor Carpi Ulnaris Muscle

If we look at the back of the forearm, we can see several muscles, including the extensor carpi ulnaris. This muscle lies along the ulnar side of the posterior forearm and contributes to its visible contour.

The extensor carpi ulnaris starts from the lateral epicondyle of the humerus and the posterior border of the ulna. Downward, the muscle passes into a long, narrow tendon that attaches to the base of the fifth metacarpal bone. When contracting, this muscle extends and adducts the hand at the wrist.

Extensor Digitorum Muscle

This is one of the largest superficial muscles of the posterior forearm. You can see this muscle even in people who are not professional athletes. The extensor digitorum starts from the lateral epicondyle of the humerus, and its four tendons pass to the fingers and join their extensor expansions.

In anatomical dissection, this muscle is often easy to identify because its tendons are large and superficially located.

Muscles of the Hand

The hand is a very mobile part of the human body. Its movements are controlled by both the forearm muscles and the intrinsic muscles of the hand. In this section, we will look at the superficial hand muscles that are most important for plastic anatomy.

For artists, the muscles that form the eminences of the thumb and little finger are especially important because they contribute directly to the visible volume of the palm.

Muscles of the Thumb

Abductor Pollicis Brevis Muscle

This muscle is located on the lateral side of the eminence of the thumb. The abductor pollicis brevis contributes to the volume of the palm because it is located directly under the skin. This muscle starts from the scaphoid and trapezium bones and the flexor retinaculum, and attaches to the lateral side of the base of the proximal phalanx of the thumb.

Flexor Pollicis Brevis Muscle

This muscle is located slightly medial to the previous muscle, also directly under the skin. The flexor pollicis brevis has superficial and deep heads. These arise from the flexor retinaculum and trapezium, as well as from the trapezoid and capitate bones. The muscle attaches to the base of the proximal phalanx of the thumb.

Muscles of the Little Finger

Palmaris Brevis Muscle

This muscle looks like a thin plate that starts from the medial edge of the palmar aponeurosis and the flexor retinaculum and inserts into the skin of the hypothenar eminence.

Abductor Digiti Minimi Muscle of Hand

This muscle is an excellent landmark because it occupies the most medial position among the muscles of the hypothenar eminence. The abductor digiti minimi muscle of the hand starts from the pisiform bone and the tendon of the flexor carpi ulnaris and attaches to the medial side of the base of the proximal phalanx of the little finger.

Palmar Aponeurosis

The palmar aponeurosis is a dense layer of connective tissue located between the skin and the deeper tissues of the palm. Distally, it divides into four longitudinal slips that extend toward the fingers.

Upper Limb Topography

The upper limb is bordered by the chest, neck, and back.

The border separating the chest and upper limb includes the depression between the deltoid and pectoralis major muscles. This depression is called the deltopectoral groove.

The border separating the upper limb and the neck follows the upper edges of the clavicles toward the acromion.

The border between the upper limb and the back follows the posterior edge of the deltoid muscle.

Upper Limb Regions

The boundaries of the deltoid region correspond to the boundaries of the deltoid muscle.

The upper arm region is bounded above by the lower edge of the deltoid muscle and below by the upper edge of the cubital region. The upper arm is subdivided into anterior and posterior regions. The anterior region corresponds mainly to the biceps brachii, while the posterior region corresponds mainly to the triceps brachii.

The cubital region has anterior and posterior parts. The anterior part includes the cubital fossa, while the posterior part includes the visible contours around the olecranon.

The forearm region is bounded above by the lower border of the cubital region and below by an imaginary line drawn through the styloid processes of the radius and ulna.

The hand begins below an imaginary line drawn through the styloid processes of the radius and ulna.

Important Topographic Landmarks

Cubital Fossa

The cubital fossa is bounded above by an imaginary line between the medial and lateral epicondyles of the humerus, medially by the pronator teres, and laterally by the brachioradialis. The brachialis and supinator muscles form its floor. The cubital fossa can sometimes be seen as a shallow depression on a living person.

Axillary Fossa

The axillary fossa is bounded anteriorly by the pectoralis major and minor muscles, posteriorly by the subscapularis, teres major, and latissimus dorsi, medially by the serratus anterior and thoracic wall, and laterally by the humerus.