The second important concept concerns the spaces that occur beneath the peritoneal covering (17). The preperitoneal space is the space bounded by the peritoneum posteriorly and the transversalis fascia anteriorly. The space of Retzius is that space between the pubis and the bladder. The lateral extent of this space is named Bogro's space. The transversalis fascia forms the floor of the inguinal canal and the iliopectineal arch, iliopubic tract, and crura of the deep inguinal ring. The iliopectineal arch divides the vascular compartment (iliac vessels) from the neuromuscular compartment (iliopsoas muscle, femoral nerve, and the lateral femoral cutaneous nerve). The iliopubic tract is an aponeurotic band that begins near the anterior superior iliac spine and inserts on the pubic tubercle (23) medially. In its medial extent, it contributes to the formation of Cooper's ligament (22). It forms the inferior margin of the deep musculoaponeurotic layer made up of the transversus abdominis muscle and aponeurosis and the transversalis fascia. Laterally, it extends to the iliacus and psoas fascia. It forms with fibers of the transversalis fascia, the anterior margin of the femoral sheath and the medial border of the femoral ring and canal. Its lower margin is attached to the inguinal ligament. The iliopubic tract is an important landmark. Dissection or tacking of preperitoneal mesh should not take place inferior to the iliopubic tract except in the limited region of Cooper's ligament. Dissection or tack placement centrally beneath the iliopubic tract will injure the femoral vein, artery, and nerve, whereas placement laterally may damage the lumbar nerve branches. The superior and inferior crura of the deep inguinal ring are formed by the transversalis fascia. Cooper's ligament is formed by the periosteum of the superior pubic ramus and the iliopubic tract.