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No. 31
1. Anterior Branches of Thoracic Nerves
2. Lumbar Plexus
3. Sacral Plexus
Ⅲ. The Anterior Branches of
Thoracic Nerves
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They are twelve in number on each side.
The upper eleven lie between the ribs and are
called the intercostal nerves.
The twelfth lies below the last rib, so it is called
the subcostal nerve.
A typical intercostal nerve runs, at first, outside
the pleura, across the internal surface of the
intercostal membrane. Close to the costal angle,
the nerve enters the fascial space between the
intercostales interni and the intercostales intimi
and continues forward along the costal groove,
where it accompanies the intercostal vessels and
lies below them.
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The upper six nerves run toward the sternum and
terminate as the anterior cutaneous branches
that pierce the intercostal muscles and the
pectoralis major near the sternum.
The lower five intercostal nerves and the
subcostal nerve cross the costal arch and
continue their course anteriorly between the
obliquus internus abdominis and transversus
abdominis. Then they pierce the sheath of rectus,
penetrate the rectus abdominis and terminate as
anterior cutaneous branches near the linea alba.
Muscular branches of these nerves supply the
intercostales and the anterolateral abdominal
muscles. The cutaneous branches are distributed
to the skin of the thoracic and abdominal wall.
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The distribution of the anterior branches
of the thoracic nerves is segmental. On
the anterior surface of the trunk, they
present about the level of:
T2-the sternal angle,
T4-the nipple,
T6-the xiphoid process ,
T8-the costal arch,
T10-the umbilicus,
T12-the anterior superior iliac spine.
Ⅳ. The Lumbar Plexus
Ⅰ) The formation of lumbar plexus
 It is formed by the anterior branches of
the first three lumbar nerves (L1-3), a
part of the anterior branches of the last
thoracic nerve (T12)and the fourth lumbar
nerve (L4).
Ⅱ) Location of lumbar plexus
 It is located anterior to the psoas major
and the transverse processes of the
lumbar vertebrae.
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Ⅲ) The branches of lumbar plexus
1. The iliohypogastric nerve (T12, L1)
Its cutaneous branch supplies the skin of the
hypogastric region and inguinal region.
Its muscular branch supplies the muscles of the
lower part of the abdominal wall.
2. The ilioinguinal nerve (L1)
It supplies the skin of scrotum (or the greater lip
of pudendum), and the muscles of lower
abdominal wall.
3. The lateral femoral cutaneous nerve (L2-3)
It supplies the skin over the anterior and lateral
parts of the thigh.
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4. The femoral nerve (L2-4)
It descends between the psoas major and the
iliacus, then passes down beneath the inguinal
ligament into the femoral triangle, where it is
“broken up” into several terminal branches.
Its muscular branches supply the anterior group
of muscles of the thigh---the quadriceps femoris,
sartorius and pectineus.
Its cutaneous branches to the thigh are the
anterior cutaneous branches which are
distributed to the anterior and anteromedial side
of the skin of the thigh.
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Saphenous nerve:
The longest one of its cutaneous branches
is the saphenous nerve. It accompanies
the femoral artery and descends through
most of the length of the adductor canal,
becomes subcutaneous at the medial side
of the knee by emerging behind the
sartorius. Then it runs downward with the
great saphenous vein along the medial
side of leg as far as the medial side of the
foot. This nerve is distributed to the skin
of the medial side of the leg and foot.
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Injury of the femoral nerve results in
impaired flexion of the hip joint. Because
the quadriceps femoris muscle is
paralyzed. It is impossible to extend knee
and the knee jerk reflex disappears. There
would also be a loss of sensation in the
skin of the anterior area of the thigh and
the medial side of the leg and foot.
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5. The obturator nerve (L2-4)
It emerges from the medial border of the psoas
major, whence it passes along the lateral pelvic
wall and through the obturator canal to the
medial part of the thigh.
The muscular branches of the nerve supply the
medial group of muscles of the thigh, the
cutaneous branches are distributed to the skin of
the medial side of the thigh.
Injury to the obturator nerve results in impaired
adduction of the thigh and a loss of sensation in
the skin of the medial aspect of the thigh.
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6. The genitofemoral nerve (L1-2)
It supplies the skin over the scrotum (or
the greater lip of pudendum), and the
cremaster.
The iliohypogastric, ilioinguinal and
genitofemoral nerves must be protected
carefully in the operation of the inguinal
hernia.
Ⅴ. The Sacral Plexus
Ⅰ) The formation of sacral plexus
 This plexus is formed by the lumbosacral
trunk (a part of L4 and L5), the anterior
branches of the sacral and coccygeal
nerves (S1-5, Co1).
Ⅱ) The location of sacral plexus
 It is located in the pelvis, where it is
closely related to the anterior surface of
the piriformis.
Ⅲ) The branches of sacral plexus
1. The superior gluteal nerve (L4-5)
 It leaves the pelvis via the greater sciatic
foramen superior to the piriformis in
company with the superior gluteal vessels,
and passes between the gluteus medius
and gluteus minimus.
 It supplies the gluteus medius and gluteus
minimus and the tensor fasciae latae.
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2. The inferior glutea nerve (L5-S2)
It leaves the pelvis through the greater
sciatic foramen inferior to the piriformis in
company with the inferior gluteal vessels.
It supplies the gluteus maximus and the
skin over the lower part of the gluteal
region.
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3. The pudendal nerve (S2-4)
It emerges from the pelvis via the greater
sciatic foramen below the piriformis in
company with the internal pudendal
vessels. It crosses the dorsum of the
sacrospinous ligament to enter the
perineum through the lesser sciatic
foramen. Then it traverses the lateral wall
of the ischiorectal fossa and gives off
branches to innervate the muscles and
skin of the perineum and the external
genital organs:
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1) The anal nerve
It is distributed to the sphincter ani externus and
skin of the anus.
2) The perineal nerve
It is distributed to the muscles of the perineum
and the skin of the scrotum or the greater lip of
pudendum.
3) The dorsal nerve of penis or clitoris
It passes to the dorsum of the penis (or clitoris).
It supplies the skin of the penis (or clitoris),
prepuce and the glans penis (or glans of clitoris).
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4. The posterior femoral cutaneous
nerve (S1-3)
It descends in company with the sciatic
nerve and is distributed to the skin of the
posterior part of the thigh.
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5. The sciatic nerve (L4-S3)
It is the largest nerve in the body.
The nerve leaves the pelvis through the greater
sciatic foramen inferior to the piriformis along
with the inferior gluteal nerve. Then it runs
inferolaterally deep to the gluteus maximus, and
descends between the ischial tuberosity and the
greater trochanter of femur to enter the posterior
compartment of the thigh. Here, it passes
downward between the biceps femoris and the
semimembranosus, semitendinosus to enter the
popliteal fossa, and terminates by dividing into
the tibial and common peroneal nerves.
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The branches of the sciatic nerve supply
the muscles of the foot, leg and the
posterior compartment of the thigh. It also
supplies the skin of the leg and foot.
The level of division of the sciatic nerve is
variable. It is usually at the superior angle
of the popliteal fossa but these two nerves
may be separated even at their origins in
the pelvis.
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1) The tibial nerve (L4-S3)
It is the large one of the two terminal branches of
the sciatic nerve.
At first the nerve descends through the center of
the popliteal fossa in company with the politeal
vessels and posterior to the popliteal vein, it then
passes deep to the triceps surae and posterior to
the medial malleolus, where the tibial nerve is
divided into the medial and lateral plantar
nerves to supply the plantar muscles and the
skin over the sole of the foot.
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In the popliteal fossa, the tibial nerve gives off
branches to all the muscles of the posterior
compartment of the leg. It also gives off a
cutaneous branch, the medial sural cutaneous
nerve, which descends in company with the
small saphenous vein.
At the lower part of the leg, the medial sural
cutaneous nerve usually joins the lateral sural
cutaneous nerve, coming from the common
peroneal nerve, to form the sural nerve which is
distributed to the skin of the posterior and lateral
surface of the leg and over the lateral border of
the dorsum of the foot.
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2) The common peroneal nerve (L4-S2)
It begins at the superior angle of the
popliteal fossa and passes lateroinferiorly
along the medial border of the biceps
femoris and its tendon. It leaves the fossa
by passing superficially to the lateral head
of the gastrocnemius. The nerve then
passes around the posterolateral surface
of the neck of fibula to enter deep to the
superior part of the peroneus longus.
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The common peroneal nerve is palpable
where it winds around the neck of fibula,
and is divided into the superficial and deep
peroneal nerves.
The common peroneal nerve supplies the
muscles of the anterior and lateral
compartments of the leg. It also gives off
branches of the skin over lateral surface of
the leg and dorsum of the foot.
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① The superficial peroneal nerve
It descends between the peroneus longus
and brevis and pierces the deep fascia to
become superficial in the distal one third
of the leg. The branches of this nerve
supply the peroneal muscles and the skin
on the distal part of the anterior surface of
the leg, the dorsum of the foot and toes.
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② The deep peroneal nerve
It is in company with the anterior tibial artery. At
first it lies between the extensor digitorum longus
and the tibialis anterior and then between the
extensor hallucis longus and the tibialis anterior.
It supplies the anterior group of muscles of the
leg and a small area of the skin between the first
and second toes.
Functional disturbances in the case of the
common peroneal nerve injuries include impaired
dorsiflex of the foot, reduced or lost eversion of
the foot. This condition causes the foot to hang
down and is known as “foot-drop” or “talipes
equinovarus”. There is also a variable loss of
sensation of the anterolateral aspect of the leg
and the dorsum of the foot.