604 THE NERVOUS SYSTEM. 
branch, in the upper part of Scarpa’s triangle. The two branches descend vertically 
and become cutaneous by piercing the fascia lata over the upper third of the 
sartorius muscle. They carry muscular branches to the sartorius, and the external 
branch in many cases pierces the muscle. These two nerves supply the skin of 
the lower three-fourths of the front of the thigh, between the external cutaneous 
nerve on the outer side and the internal cutaneous on the inner side. They reach 
down to the front of the patella, and there assist in the formation of the patellar 
plexus. The external branch communicates in the upper third of the thigh with 
twigs from the crural branch of the genito-crural nerve. 
The internal cutaneous nerve lies at first in Scarpa’s triangle on the outer side 
of the femoral vessels. At the apex of the triangle it crosses over the femoral vessels, 
and is directed downwards over or through the sartorius muscle, and beneath the 
fascia lata to the lower third of the thigh. It is distributed to the skin of the 
lower two-thirds of the thigh on the inner side by means of three branches—upper, 
middle, and lower. 
The upper branch may be represented by two or more twigs. It arises from the 
inain nerve near its origin, and pierces the fascia lata near the apex of Scarpa’s 
triangle. It is distributed to the skin of the upper part of the thigh, along the 
line of the saphenous vein. The middle or anterior branch is a larger nerve. It 
separates from the lower branch at the apex of Scarpa’s triangle, and passing over 
the sartorius muscle becomes cutaneous in the middle third of the thigh on the 
inner side. It supphes the skin of the lower half of the thigh on the inner side, 
extending as low as the knee, where it joins in the formation of the patellar 
plexus. 
The lower or internal branch represents the termination of the nerve. It passes 
down the inner side of the thigh over the sartorius muscle, and communicates in 
the middle third of the thigh with the internal saphenous and obturator nerves to 
form the obturator plexus. Piercing the fascia lata on the inner side of the thigh 
in the lower third, it ramifies over the inner side of the knee, and assists in the 
formation of the patellar plexus. 
The size of the internal cutaneous nerve varies with the size of the cutaneous 
part of the obturator, and of the internal saphenous nerve. 
The long or internal saphenous nerve (un. saphenus) may be regarded as the 
terminal branch of the anterior crural nerve. It is destined for the skin of the leg 
and foot. From its origin in Scarpa’s triangle it descends alongside the femoral 
vessels to Hunter’s canal. In the canal it crosses over the femoral sheath from 
without inwards. At the lower end of the canal, accompanied by the superficial 
branch of the anastomotic artery, 1t passes over the tendon of the adductor magnus, 
and opposite the inner side of the knee joint becomes cutaneous by passing between 
the sartorius and gracilis muscles. The nerve then extends down the leg along 
with the internal saphenous vein, and coursing over the front of the inner ankle it 
terminates at the middle of the inner border of the foot. 
Branches.—1. A communicating branch arises in Hunter's canal, and passing 
inwards beneath the sartorius joins with branches of the obturator nerve in forming 
the obturator plexus. 
The patellar branch arises at the lower end of Hunter’s canal, and piercing the 
sartorius muscle is directed downwards and forwards below the patella, and over 
the inner tuberosity of the tibia to the front of the knee and upper part of the 
lee. It enters into the formation of the patellar plexus. 
3. An articular branch sometimes arises from the nerve at the inner side of the 
knee. 
4. The terminal branches of the internal saphenous nerve are distributed to the 
skin of the front and inner side of the leg, and the posterior half of the dorsum 
and inner side of the foot. 
Patellar plexus—This plexus consists of fine communications beneath the 
skin in front of the knee, between the branches of the cutaneous nerves supplying 
that region. The nerves which enter into its formation are the patellar branch of 
the internal saphenous, internal and middle cutaneous nerves, and sometimes the 
external cutaneous nerve. 
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