**Core Concept:** The pectoralis major muscle is a large, fan-shaped muscle located in the anterior chest wall, responsible for clavicular and sternal chest movements. It is innervated by specific branches from the thoracic nerves.

**Why the Correct Answer is Right:** The pectoralis major muscle is supplied by the pectoral branches of the thoracic nerves. These branches originate from the first to fifth thoracic nerves and supply the muscle with motor and sensory nerves, enabling muscle contraction and sensation.

**Why Each Wrong Option is Incorrect:**

A. Thoracoacromial artery is not responsible for supplying blood to the pectoralis major muscle. It is a branch of the internal mammary artery, supplying the skin, subcutaneous tissue, and the overlying pectoralis major muscle.

B. Intercostal nerves are responsible for supplying motor and sensory innervation to the intercostal muscles and skin of the anterior chest wall, not pectoralis major.

C. Lateral thoracic artery supplies the skin and subcutaneous tissue of the lateral chest wall but not the pectoralis major muscle.

D. Subclavian artery supplies the skin, subcutaneous tissue, and first rib but not the pectoralis major muscle.

**Clinical Pearl:** In clinical practice, understanding the anatomy of chest wall innervation is essential for managing post-surgery complications or diagnosing neuropathies, such as recognizing the typical distribution of injury signs for each thoracic nerve level.

**Correct Answer:** 1. Pectoral branches of thoracoacromial artery (Thoracoacromial artery is the correct answer, not thoracoacromial artery).