250 THE ABDOMEN AND PELVIS 



gall-bladder through the right rectus, and to the stomach 

 through the left rectus. The direction of the incision may 

 vary as it passes through the skin and fascia, but the anterior 

 layer of the sheath and the muscle are split vertically, i.e. 

 parallel to the muscular fibres, or the rectus may be freed and 

 retracted. Finally, the posterior layer of the sheath and the 

 muscular fibres of the trans versus (p. 246) are divided, together 

 with the subjacent and partially adherent fascia trans versalis. 

 This exposes the extra-peritoneal fat, which forms a layer of 

 considerable thickness in this region. After it has been cut 

 through, the parietal peritoneum becomes visible. 



In the lower third, this route may be employed for 

 appendicectomy. As soon as the rectus is split or retracted, 

 the fascia transversalis is exposed, as the posterior wall of the 

 sheath is deficient in this region (p. 246). The inferior (deep) 

 epigastric artery, which lies on the fascia transversalis (p. 253), 

 is also exposed, and it may either be retracted or ligated. The 

 extra-peritoneal fat is very scanty, and may only be represented 

 by a little areolar tissue. 



Occasionally, e.g. for the removal of large tumours of the 

 kidney or malignant growths of the colon, it may be necessary 

 to cut through the lateral abdominal muscles in a vertical 

 direction ; i.e. across the muscular fibres. The incision com- 

 mences above at the lower border of the tenth costal cartilage, 

 and descends towards the anterior superior iliac spine. Below, 

 it passes medially, above the inguinal ligament. It penetrates 

 all the muscles of the abdominal wall along the same line and 

 is limited, medially, by the inferior (deep) epigastric artery and 

 the abdominal inguinal (int. abd.) ring. 



The Nerves of the Abdominal Wall run in the interval 

 between the internal oblique and the transversus abdominis 

 the upper, horizontally ; the lower, downwards and medially. 

 After they leave the costal margin, the seventh and eighth 

 intercostal nerves run upwards and medially behind the rectus, 

 while the ninth and tenth run transversely. The nerves of the 

 abdominal wall include the lower seven thoracic nerves and the 

 first lumbar nerve, which is represented by two branches, the 

 ilio-hypogastric and the ilio-inguinal. As they pass forwards 

 they supply the lateral muscles of the abdominal wall, and at 

 the linea semilunaris all, save the ilio-hypogastric and ilio- 

 inguinal, enter the rectus sheath. Finally they supply the 

 rectus muscle, and pierce it to become cutaneous (p. 240). 



