Final answer:
The Obturator nerve is the nerve that passes medially to the Psoas Major muscle and innervates the medial thigh muscles.
Step-by-step explanation:
The nerve that passes medially to the Psoas Major muscle and innervates the medial thigh muscles is the Obturator nerve(b). This nerve provides sensory and motor innervation to the medial thigh muscles including the adductor longus, adductor brevis, and adductor magnus which are involved in medially and laterally rotating the thigh, flexing and extending it. The Obturator nerve is essential for movements such as adducting the thighs. In contrast, the Femoral nerve (a), located in the femoral triangle alongside the femoral artery and vein, innervates the anterior compartment of the thigh which includes the quadriceps femoris and sartorius muscles. The Sciatic nerve (c) and Genitofemoral nerve (d) do not innervate the medial thigh muscles.