The Ilioinguinal Nerve (n. ilioinguinalis), smaller than the Iliohypogastric Nerve, arises with it from the first lumbar nerve.
It emerges from the lateral border of the Psoas major just below the iliohypogastric, and, passing obliquely across the Quadratus lumborum and Iliacus, perforates the Transversus abdominis, near the anterior part of the iliac crest, and communicates with the iliohypogastric nerve between the Transversus and the Obliquus internus.
The nerve then pierces the Obliquus internus, distributing filaments to it, and, accompanying the spermatic cord through the subcutaneous inguinal ring, is distributed to the skin of the upper and medial part of the thigh, to the skin over the root of the penis and upper part of the scrotum in the male, and to the skin covering the mons pubis and labium majus in the female.
The size of this nerve is in inverse proportion to that of the iliohypogastric. Occasionally it is very small, and ends by joining the iliohypogastric; in such cases, a branch from the iliohypogastric takes the place of the ilioinguinal, or the latter nerve may be altogether absent.