In the adult this canal is about 1 1/2 inches long, (Fig. XX, 19.) and extends from the internal to the external abdominal rings. (Fig. XX, 17.)
The internal abdominal ring, a funnel-shaped prolongation of the transversalis fascia, is situated 1/2 inch above the midpoint of Poupart's ligament. The external abdominal ring, (Fig. XX, 18.) formed by the splitting of the aponeurosis of the external oblique muscle, is triangular in shape, the base directed downwards and inwards and opening up immediately above the pubic spine, whilst the apex is directed upwards and outwards.
This triangle is bounded in front by the posterior border of the external oblique, and behind by the anterior border of the latissimus dorsi muscle, whilst the base is formed by part of the iliac crest. The external oblique is inserted into the anterior half of the iliac crest, and the base of the triangle corresponds to 1 to 2 inches of the bone behind the mid-point of the crest. The triangle is subject to great variation in size, the two bounding muscles converging rapidly above to form the apex of the triangle. The floor is formed by the internal oblique muscle.