THE ABDOMINAL WALLS 275 



above the lateral part of the inguinal ligament, being limited 

 by the abdominal inguinal (int. abd.) ring. 



The lower fibres of the latissimus dorsi are cut across, exposing 

 the lumbo-dorsal fascia above and the internal oblique below. 

 These structures are divided in the line of the skin incision, and 

 the lateral part of the wound is deepened through the transversus 

 abdominis until the fascia trans versalis is reached. The pos- 

 terior layer of the peri-nephric fascia, which is the continuation 

 of the fascia transversalis in a medial direction, has already been 

 exposed by the division of the lumbo-dorsal fascia. It is now 

 incised, and the kidney and the commencement of the ureter 

 are found in the peri-renal fat. As the ureter is traced down- 

 wards, it becomes necessary to divide the fascia transversalis, 

 which has so far been preserved intact. This is done with great 

 care because, owing to the scantiness of the extra-peritoneal 

 fat in this region, there is danger of opening the peritoneal 

 cavity. In addition, the descending colon is retro-peritoneal 

 and the posterior wall of the gut or its blood-vessels may be 

 injured unless great care is exercised. 



When the whole incision is employed, the ureter can be 

 traced from its commencement in Gerota's space through the 

 anterior layer of the peri-nephric fascia into the extra-peritoneal 

 fat, and then downwards to the pelvis. 



In the process, the peritoneum is stripped off the posterior 

 abdominal wall and serves to keep the abdominal contents 

 away from the field of the operation. 



The danger of opening the pleural sac at the upper end of 

 the wound must also be borne in mind. The lower limit of the 

 sac posteriorly (p. 509) lies in front of the last rib, at the point 

 where the rib is crossed by the lateral margin of the sacro-spinalis. 

 Frequently the last rib is so short that its extremity cannot be 

 felt. In these cases the eleventh rib may be mistaken for the 

 twelfth, and if so, the pleura will be opened at the upper part 

 of the wound as the incision is deepened. This danger can be 

 avoided by counting the ribs from above downwards and so 

 determining whether the lowest palpable rib is the eleventh or 

 the twelfth. Further, on rare occasions, the pleura may lie at 

 a lower level than normal, and cross the apex of the angle between 

 the twelfth rib and the sacro-spinalis. It is then very difficult 

 to avoid opening the pleural sac. 



It may be necessary, e.g. after radiographic localisation of 

 ureteral calculi, to expose the ureter without exploring the kidney, 



