The internal inguinal ring is the entrance to the inguinal canal. Its surface markings are 1 to 1.5cm superior to the mid-inguinal point.
Its borders are:
- superolateral: internal oblique and transversus abdominis muscles
- medial: inferior epigastric vessels and interfoveolar ligament
- inferior: inguinal ligament
It lies lateral to the inferior epigastric vessels as they pass upwards from the external iliac artery and vein. It is the point at which the spermatic cord or round ligament push through the transversalis fascia.
The transversalis fascia forms a U-shaped sling around the ring with two crura:
- antero-superior crus is continuous with the transversus abdominis muscle and its aponeurosis
- postero-inferior crus is continuous with inguinal ligament
The angulation of the ring and contraction of transversus abdominis act like a valve to prevent herniation in normal individuals.