The superficial inguinal ring, known alternately as the subcutaneous or external inguinal ring, is a small opening between the layers of soft tissue in the lower abdominal wall. It is the outermost opening — that nearest the skin — to the inguinal canal, a tunnel through which multiple nerves and reproductive vessels pass. This exit from the inguinal canal is lower than its entrance, the deep inguinal ring. Though it is referred to as a ring, the superficial inguinal ring is triangular in shape where it exits the aponeurosis of the external oblique muscle.
Beneath the skin and fat covering the front of the pelvis are layers of connective tissue called aponeuroses. These flat, stretched layers of fibrous tissue join the individual abdominal muscles — the rectus abdominis, obliquus externus, obliquus internus, and transversus abdominis — to the anterior or front aspect of the pelvis. Since each aponeurosis covers only a portion of the lower abdomen, crisscrossing as they layer over each other, openings like the superficial inguinal ring are exposed between them where vessels can push through en route from the abdomen to the pelvis.
One such opening is the inguinal canal, whose entrance, the deep inguinal ring, begins deep to the transversus abdominis muscle in a layer of tissue known as the transversalis fascia. The transversalis fascia separates the transverse abdominis, the deepest of the four abdominal muscles, from the peritoneum, the membrane containing the organs of the abdominal cavity. At the approximate mid-point of the inguinal crease, the line from the hipbones to the pubic bone that demarcates where the leg meets the body, is where the deep inguinal ring opens to the inguinal canal.
The inguinal canal then passes downward and inward at an angle roughly parallel to that of the inguinal crease, approaching the skin as it descends. Crossing below the transversus abdominus and internal oblique muscles and their respective aponeuroses, it approaches the aponeurosis of the external oblique muscle from behind. Within this tunnel are housed two nerves, the ilioinguinal and genitofemoral nerves, and in men the spermatic cord and in women the round ligament. The spermatic cord leads to the scrotum, while the round ligament is a ligament that extends to the labia majora and helps to hold the uterus in position in the pelvic cavity. Due to the diameter of the spermatic cord, the inguinal canal has a more substantial width in men than in women.
Forming the lower exit point of the inguinal canal from which these vessels emerge is the superficial inguinal ring. It emerges through the fibers of the lower border of the aponeurosis of the external oblique and sits just above the inguinal ligament, which follows the inguinal crease. The fibers it shares with these tissues along its borders are known as the crura. Superficial to the pubis bone in the anterior lower pelvis, the superficial inguinal ring is found immediately above the crest of the pubis and just to the outside of a projection on the pubis known as the pubic tubercle.
