The topic covers the detailed anatomy of the upper limb muscles, focusing on their roles in movement and stability. The upper limb muscles are divided into different groups based on their location and function:

### 1. **Shoulder Muscles (Musculi Humeri)**

The shoulder muscles surround the shoulder joint, with the **rotator cuff** being crucial for movement and stability. Key muscles include:

- **Supraspinatus**: Abducts the arm at the shoulder, innervated by the suprascapular nerve.

- **Infraspinatus** and **Teres Minor**: Both muscles externally rotate the arm, innervated by the suprascapular and axillary nerves.

- **Subscapularis**: Internally rotates the arm, innervated by the subscapular nerves.

### 2. **Arm Muscles (Musculi Brachii)**

The arm muscles are split into anterior and posterior groups.

#### Anterior Group:

- **Biceps Brachii**: Flexes the elbow and supinates the forearm, innervated by the musculocutaneous nerve.

- **Brachialis**: Primary elbow flexor, innervated by the musculocutaneous and radial nerves.

- **Coracobrachialis**: Flexes and adducts the arm, innervated by the musculocutaneous nerve.

#### Posterior Group:

- **Triceps Brachii**: Extends the elbow, innervated by the radial nerve.

### 3. **Forearm Muscles (Musculi Antebrachii)**

The forearm muscles control wrist and finger movements and are divided into anterior, lateral, and posterior groups.

#### Anterior Group:

- **Superficial Layer**: Includes **Flexor Carpi Radialis**, **Palmaris Longus**, and **Pronator Teres** that control wrist flexion and forearm pronation.

- **Deep Layer**: Flexes fingers and thumb, including **Flexor Digitorum Superficialis** and **Flexor Pollicis Longus**.

#### Lateral Group:

- **Brachioradialis**: Flexes the elbow, innervated by the radial nerve.

- **Extensor Carpi Radialis Longus and Brevis**: Extend and abduct the wrist.

#### Posterior Group:

- **Extensor Digitorum**: Extends the fingers.

- **Supinator**: Supinates the forearm.

### 4. **Hand Muscles (Musculi Manus)**

The hand muscles are responsible for fine motor control and are divided into three groups:

#### Thenar Muscles (Thumb Movement):

- **Abductor Pollicis Brevis**, **Flexor Pollicis Brevis**, **Opponens Pollicis**, and **Adductor Pollicis** control thumb movements, innervated by the median and ulnar nerves.

#### Hypothenar Muscles (Little Finger Movement):

- **Abductor Digiti Minimi**, **Flexor Digiti Minimi**, and **Opponens Digiti Minimi** control little finger movements, innervated by the ulnar nerve.

#### Intermediate Muscles:

- **Lumbricals**: Flex the metacarpophalangeal joints and extend interphalangeal joints.

- **Interossei**: Control finger abduction (dorsal) and adduction (palmar), innervated by the ulnar nerve.

### 5. **Axillary Region (Armpit)**

The axillary region is a pyramidal space between the upper arm and chest, housing critical structures like the **axillary artery**, **brachial plexus**, and **axillary lymph nodes**. It is bounded by:

- **Anterior Wall**: Pectoralis major muscle.

- **Posterior Wall**: Latissimus dorsi, teres major, and subscapularis muscles.

- **Medial Wall**: Serratus anterior muscle.

- **Lateral Wall**: Humerus.

The axillary space allows the passage of vital nerves and blood vessels to the upper limb, making it an essential structure for upper limb function.

In summary, the upper limb's anatomy consists of several muscle groups that work together to enable a wide range of movements, from gross motor functions like shoulder abduction and elbow extension to fine motor skills in the hand. The axillary region serves as a passageway for critical structures that support these functions.