Which muscle is located deep to the latissimus dorsi and has finger-like projections running from the ribs to the scapula?
Pectoralis minor
Serratus anterior
Xiphihumeralis
Rectus abdominis
The correct answer and explanation is :
The correct answer is Serratus anterior.
Explanation:
The serratus anterior is a muscle located deep to the latissimus dorsi, primarily responsible for the protraction and upward rotation of the scapula. It originates from the upper eight or nine ribs and inserts onto the medial border of the scapula.
Key Characteristics:
- Finger-like projections: The serratus anterior has a distinctive appearance due to its multiple digitations (finger-like projections) that extend from the lateral surface of the ribs to the scapula. These projections give it a serrated look, which is why it is named “serratus.”
- Deep to Latissimus Dorsi: The latissimus dorsi is a large, superficial back muscle that covers much of the lower back. The serratus anterior, however, lies beneath this muscle, along the lateral thoracic wall.
- Function:
- It protracts the scapula (pulls it forward), which is crucial in pushing movements (e.g., punching, earning it the nickname “boxer’s muscle”).
- It assists in upward rotation of the scapula, allowing full arm elevation above the head.
- It stabilizes the scapula against the thoracic wall, preventing “winged scapula,” a condition seen when the muscle is weak or paralyzed.
- Innervation: The long thoracic nerve (C5-C7) controls the serratus anterior. Damage to this nerve can lead to scapular winging, where the scapula protrudes abnormally from the back.
Why Not the Other Options?
- Pectoralis minor: Lies deep to the pectoralis major and does not have finger-like projections from the ribs.
- Xiphihumeralis: A muscle found in some animals, like cats, but not in humans.
- Rectus abdominis: A muscle in the anterior abdominal wall, unrelated to scapular movement.
Thus, the serratus anterior is the correct answer.