The subsartorial plexus is a plexus

Nerve plexus

A nerve plexus is a network of intersecting nerves. Except for the ventral rami of Th2-Th11 nerves, they combine sets of ventral rami of spinal nerves that serve the same area of the body into one large grouped nerve...

 of nerves that is located under the sartorius muscle

Sartorius muscle

The Sartorius muscle – the longest muscle in the human body – is a long thin muscle that runs down the length of the thigh. Its upper portion forms the lateral border of the femoral triangle.-Origin and insertion:...

. It is formed by:

1. the medial cutaneous nerve of the thigh (a branch of the femoral nerve
   Femoral nerve
   The femoral nerve, the largest branch of the lumbar plexus, arises from the dorsal divisions of the ventral rami of the second, third, and fourth lumbar nerves...
   
   )
2. the saphenous nerve
   Saphenous nerve
   The saphenous nerve is the largest cutaneous branch of the femoral nerve.-Path:It approaches the femoral artery where this vessel passes beneath the sartorius, and lies in front of the artery, behind the aponeurotic covering of the adductor canal, as far as the opening in the lower part of the...
   
    (a branch from femoral nerve)
3. the cutaneous branch of anterior division of the obturator nerve
   Cutaneous branch of the obturator nerve
   Occasionally the communicating branch to the anterior cutaneous and saphenous branches of the femoral is continued down, as a cutaneous branch, to the thigh and leg, as the cutaneous branch of the obturator nerve....
   
   

At the lower border of the adductor brevis muscle

Adductor brevis muscle

The adductor brevis is a muscle in the thigh situated immediately behind the pectineus and adductor longus.-Origin and insertion:It is somewhat triangular in form, and arises by a narrow origin from the outer surfaces of the superior and inferior rami of the pubis, between the gracilis and...

 the cutaneous branch of anterior division of the obturator nerve communicates with the anterior (medial), cutaneous and saphenous branches of the femoral nerve, forming a kind of plexus. It then descends upon the femoral artery

Femoral artery

The femoral artery is a general term comprising a few large arteries in the thigh. They begin at the inguinal ligament and end just above the knee at adductor canal or Hunter's canal traversing the extent of the femur bone....

, to which it is finally distributed.

Occasionally the communicating branch to the anterior (medial), cutaneous and saphenous branches of the femoral is continued down, as a cutaneous branch, to the thigh and leg. When this is so, it emerges from beneath the lower border of the Adductor longus muscle

Adductor longus muscle

In the human body, the adductor longus is a skeletal muscle located in the thigh. One of the adductor muscles of the hip, its main function is to adduct the thigh and it is innervated by the obturator nerve...

, descends along the posterior margin of the Sartorius to the medial side of the knee, where it pierces the deep fascia

Deep fascia

Deep fascia is a layer of fascia which can surround individual muscles, and divide groups of muscles into compartments....

, communicates with the saphenous nerve, and is distributed to the skin of the tibial side of the leg as low down as its middle.