1. No. 31 1. Anterior Branches of Thoracic Nerves 2. Lumbar Plexus
3. Sacral Plexus

2. Ⅲ. The Anterior Branches of Thoracic Nerves
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.

5. 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.

6. 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.

7. 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.

8. 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.

11. 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.

13. 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.

15. 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.

16. 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.

20. 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.

22. 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.

23. 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.

25. 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.

26. 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:

28. 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).

29. 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.

30. 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.

32. 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.

33. 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.

35. 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.

36. 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.

38. 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.

39. 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.

40. 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.