**Question:** All of the following muscles are derived from 6th brachial arch EXCEPT:

A. **Ansa cervicalis (Coracobrachialis)**
B. **Biceps brachii**
C. **Triceps brachii**
D. **Subscapularis**

**Core Concept:** The brachial arch is a developmental structure in humans, consisting of six pairs of somites that give rise to various structures, including skeletal muscles. In the upper limb, the sixth brachial arch contributes to the formation of muscles that are involved in shoulder and elbow movements.

**Why the Correct Answer is Right:** The correct answer, D. Subscapularis, is derived from the second and third intercostal muscles, not the sixth brachial arch. The subscapularis muscle plays a role in internal rotation and adduction of the humerus at the glenohumeral joint.

**Why Each Wrong Option is Incorrect:**

A. Ansa cervicalis, or coracobrachialis, is a short head of the triceps brachii muscle, which derives from the first thoracic and first cervical segments, not the sixth brachial arch. It plays a role in flexion at the elbow joint.

B. Biceps brachii is derived from the first and second cervical somites, not the sixth brachial arch. It is involved in flexion at the elbow joint.

C. Triceps brachii is derived from the first and second cervical segments, not the sixth brachial arch. It plays a role in extension of the elbow joint.

**Clinical Pearl:** Understanding muscle development from different somites and their functions is crucial for understanding musculoskeletal anatomy and its clinical implications in diagnosing and treating musculoskeletal disorders.

**Correct Answer:** D. Subscapularis (Letter D)

**Explanation:** The subscapularis muscle is derived from the second and third intercostal muscles, not the sixth brachial arch. It plays a role in internal rotation and adduction of the humerus at the glenohumeral joint.