The most caudal of the abdominal wall nerves are derived from the first lumbar nerve; they are the ilio-hypogastric and ilio-inguinal nerves. The ilio-inguinal nerve is generally smaller than the ilio-hypogastric nerve - if one is large the other is smaller and vice versa. Occasionally the ilio-inguinal nerve is very small and may be absent. The anterior cutaneous branch of the ilio-hypogastric nerve emerges through the aponeurosis of the external oblique just above the superficial inguinal ring and innervates the skin in the suprapubic region. The ilio-inguinal nerve passes through the lower inguinal canal and becomes superficial by emerging from the superficial inguinal ring to supply the skin of the scrotum and a small area of the medial upper thigh.
The genitofemoral nerve arises from the first and second lumbar nerves and completes the innervation of the abdominal wall and groin areas. At first it passes obliquely forwards and downwards through the substance of the psoas major. It emerges from the muscle and crosses its anterior surface deep to the peritoneum, going behind, posterior to, the ureter. It divides a variable distance from the deep inguinal ring into a genital and a femoral branch. The genital branch, a mixed motor and sensory nerve, crosses the femoral vessels and enters the inguinal canal at or just medial to the deep ring. The nerve penetrates the fascia transversalis of the posterior wall of the inguinal ligament either through the deep ring or separately medially to the deep ring. The nerve traverses the inguinal canal lying between the spermatic cord above and the upturned edge of the inguinal ligament inferiorly; the nerve is vulnerable to surgical trauma as it progresses along the floor of the canal (the gutter produced by the upturned internal edge of the inguinal ligament). The genital nerve supplies the motor function to the cremaster muscle and the sensory function to the skin of the scrotum. The femoral branch enters the femoral sheath lying lateral to the femoral artery and supplies the skin of the upper part of the femoral triangle.
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