THE ABDOMINAL WALLS 239 



surface by a curved furrow the linea semilunaris. It com- 

 mences below at the pubic tubercle and passes midway between 

 the umbilicus and the anterior superior iliac spine. It then 

 runs upwards and slightly medially, crossing the costal margin 

 near the tip of the ninth costal cartilage. Transverse furrows 

 may sometimes be seen crossing the upper part of the rectus. 

 They correspond to the lineae transversse (p. 246). 



The posterior superior iliac spine may be found by tracing 

 the iliac crest backwards. Its situation is marked by a dimple, 

 which lies i| inches from the middle line. It is placed opposite 

 the middle of the sacro-iliac joint and on a level with the second 

 sacral spine. 



The spines of the lumbar vertebrae lie at the bottom of the 

 spinal furrow, but they are rendered visible when the trunk is 

 flexed. On each side of the furrow is the prominence due to 

 the sacro-spinalis (erector spincz) muscle, the lateral margin of 

 which can be felt, and sometimes seen, at a distance of 3^ inches 

 from the middle line. The tip of the twelfth rib can be recognised 

 as it emerges from under cover of this border. It lies about 

 two inches above the midpoint of the iliac crest, but it must be 

 remembered that the lowest palpable rib is not necessarily the 

 twelfth, which is often rudimentary and completely hidden by 

 the sacro-spinalis. 



The Subcutaneous Inguinal Ring (Ext. Abdom. Ring), 

 through which the spermatic cord leaves the inguinal canal, 

 lies immediately above the pubic tubercle (spine) and may 

 be examined by invaginating the skin of the scrotum from 

 below. The anterior surface of the pubis is palpated, and the 

 finger is carried upwards until the pubic crest is reached. It is 

 then pressed backwards into the anterior abdominal wall, and 

 can be felt to pass into a yielding gap, which possesses sharp 

 and definite margins the subcutaneous inguinal ring. If the 

 finger is carried upwards, after reaching the upper border of 

 the pubis, it can be moved about quite freely under the skin 

 and fasciae of the anterior abdominal wall. 



To aid topographical description, the abdomen is subdivided into regions 

 by two transverse and two vertical planes, (a) The Subcostal Plane passes 

 horizontally through the body at the level of the most dependent parts of the 

 tenth costal cartilages ; it lies on a level with the upper part of the third 

 lumbar vertebra, (ti) The Intertubercular Plane passes horizontally through 

 the tubercles of the iliac crests ; it corresponds in level with the upper part of 

 the fifth lumbar vertebra, (c) The Right and (d) the Left Lateral Planes 

 are at right angles to the transverse planes, and each bisects the line joining 

 the anterior superior iliac spine to the symphysis pubis. 



