**Question:** Which of the following is not supplied by the superior gluteal nerve:

A. Gluteus maximus muscle
B. Obturator internus muscle
C. Piriformis muscle
D. Sartorius muscle

**Core Concept:** The superior gluteal nerve is a terminal branch of the lumbar plexus, originating from L2-L3 and L4 spinal nerves. It supplies motor and sensory innervation to the gluteal region, posterior thigh, and knee joint capsule.

**Why the Correct Answer is Right:** The superior gluteal nerve primarily supplies the gluteal muscles, specifically the gluteus maximus muscle. The other options are:

**Option A (Gluteus maximus muscle):** The gluteus maximus muscle is supplied by the superior gluteal nerve, making it the correct answer to exclude.

**Option B (Obturator internus muscle):** The obturator internus muscle is supplied by the obturator nerve, which is a separate nerve derived from the second, third, and fourth lumbar nerves.

**Option C (Piriformis muscle):** The piriformis muscle is supplied by the superior gluteal nerve, making it incorrect.

**Option D (Sartorius muscle):** The sartorius muscle is supplied by the femoral nerve, which is derived from the L1-L4 spinal nerves and is separate from the superior gluteal nerve.

**Why Each Wrong Option is Incorrect:**

Option A (Gluteus maximus muscle): The gluteus maximus is a large muscle responsible for hip abduction and extension, and contributes to knee flexion. It receives motor innervation from the superior gluteal nerve, making it incorrect in this context.

Option B (Obturator internus muscle): The obturator internus is part of the obturator muscle group, which includes the obturator externus and the adductor longus muscles. These muscles are supplied by the obturator nerve, a separate nerve derived from the second, third, and fourth lumbar nerves.

Option C (Piriformis muscle): The piriformis muscle is responsible for rotating the femur and providing external rotation of the hip joint. It receives motor innervation from the superior gluteal nerve, making it incorrect in this context.

Option D (Sartorius muscle): The sartorius muscle is a long, thin muscle that crosses the hip joint and acts as an extensor of the knee joint. It receives motor innervation from the femoral nerve, which is derived from the L1-L4 spinal nerves and is separate from the superior gluteal nerve.

**Clinical Pearls:**

1. Understanding the anatomy and innervation of muscles is crucial for clinical assessment and differential diagnosis in musculoskeletal examination. A thorough examination of the gluteal region requires an understanding of the superior gluteal nerve's function and distribution.
2. The superior gluteal nerve innervates the gluteal muscles (gluteus medius, minimus, and the gluteus maximus) and the knee flexor