(THE ABDOMINAL CAVITY. 1411 



tween the two deep muscles, run in a medial and slightly downward direction, 

 so that it is practically impossible to avoid dividing one or other of them. 



In the iliac regions, to reach the csecurn and vermiform process on the right side, 

 and the pelvic colon on the left side (colostomy), it is customary, by using what 

 is known as the " gridiron incision," to split the three abdominal muscles in the 

 direction of their fibres. The external oblique is split in the direction of the skin 

 incision, which is made obliquely from above downwards and medially. After 

 retracting the edges of this muscle the fibres of the internal oblique and trans- 

 versalis muscles are split horizontally. The abdomen is then opened by dividing 

 the transversalis fascia and peritoneum. If a comparatively large opening is 

 required the branch of the deep circumflex iliac artery, which ascends between the 

 internal oblique and trans versus muscles, a little medial to the anterior superior 

 iliac spine, is divided and ligatured, while the ilio-hypogastric and ilio-inguinal 

 nerves are to be avoided. If it is necessary to extend the incision in a medial 

 direction, the lateral part of the anterior layer of the sheath of the rectus is opened 

 and the rectus muscle retracted medially; while the inferior epigastric artery, 

 now exposed, is pushed aside or ligatured before the opening in the fascia trans- 

 versalis and peritoneum is enlarged. 



DISTRIBUTION OF SENSORY NERVES IN ANTERIOR ABDOMINAL WALL. 



A knowledge of the segmental distribution of the sensory fibres of the anterior 

 rami of the lower intercostal nerves enables us to appreciate the significance of the 

 so-called girdle pain often associated with lesions of the spinal medulla and its 

 nerve-roots. In tuberculous disease of the vertebral column, for example, the 

 girdle pain may be an early symptom of the disease, and when present it affords 

 a valuable guide to the situation of the disease in the vertebral column. The 

 seventh thoracic nerve supplies the skin at the level of the epigastric triangle, the 

 eighth and ninth, that between it and the umbilicus, the tenth that at the level of 

 the umbilicus, the eleventh and twelfth that between the umbilicus and groin. 



I Subdivisions of the Abdominal Cavity. To simplify the topography of the 

 ominal viscera the abdomen is arbitrarily divided into nine regions by two 

 horizontal and two vertical planes. Of the two horizontal planes, the superior or 

 infracostal plane is at the level of the lowest part of the tenth costal cartilages ; 

 the inferior or intertubercular plane is at the level of the tubercles of the iliac crests. 

 The two vertical planes correspond upon the surface to a line drawn vertically 

 upwards on each side from a point midway between the anterior superior iliac 

 spine and the pubic symphysis. Superiorly, these vertical planes generally strike 

 the tip of the ninth costal cartilages. The subdivisions of the superior zone are 

 termed the epigastric and right and left hypochondriac regions, of the middle zone 

 the umbilical and right and left lumbar regions, of the inferior zone the hypogastric 

 and right and left iliac regions. The epigastric, umbilical, and hypogastric regions 

 may be further divided into right and left halves by the median plane. The 

 xiphisternal junction is on a level with the fibro-cartilage between the ninth and 

 tenth thoracic vertebrae. The infracostal plane passes through the superior part of 

 the third lumbar vertebra; the intertubercular plane through the fifth lumbar 

 vertebra, about one inch above the sacral promontory. The umbilicus is situated 

 usually from one to two inches above the intertubercular line. 



In the method of surface topography employed by Addison the plane of separa- 

 tion between the superior and middle abdominal zones is placed midway between 

 the superior border of the manubrium sterni and the superior border of the pubic 

 symphysis. It will be found to lie at or near the mid-point between the xiphisternal 

 junction and the umbilicus. Posteriorly, this plane strikes the inferior border 

 of the first lumbar vertebra, and it passes so constantly through the pylorus that it 



r with advantage be termed the transpyloric plane. 

 The peritoneal cavity may be regarded as a large and complicated lymph sac 

 ch is intimately related to the abdominal viscera, and more especially to the 



THE ABDOMINAL CAVITY. 



