The structure indicated is the pectineus muscle.

The pectineus muscle is one of six muscles in the medial compartment of the thigh. The thigh consists of three muscular compartments:

1. Anterior
2. Medial
3. Posterior

The medial compartments consists of the following muscles:

• Gracilis
• Pectineus
• Adductor longus
• Adductor brevis
• Adductor magnus
• Obturator externus

All the muscles of the medial compartment are innervated by the obturator nerve except for the pectineus (femoral nerve) and the hamstring part of the adductor magnus (tibial division of sciatic). The muscles of the medial compartment generally serve to adduct the thigh at the hip joint. Due to the innervation of the pectineus muscle by the femoral nerve, it is sometimes classified as a muscle of the anterior compartment of the thigh.

Origin: Pectineal line of pubic bone

Insertion: Upper medial haft of femur

Action: Adducts hip and flexes hip

Innervation: Femoral nerve

Learn more about the anatomy of the thigh muscles in this tutorial.