198 ABDOMEN 



frequently raised to form a little button-like knob. It forms 

 part of the linea alba, and is the result of the closure of the 

 umbilical orifice which existed in the abdominal wall, up to 

 the period of birth, for the passage of the constituents of the 

 umbilical cord, viz. the allantois, the umbilical vein, and 

 the two umbilical arteries. The dissector should remember 

 that the allantois was connected with the urinary bladder, the 

 umbilical vein with the liver, and the umbilical arteries with 

 the hypogastric arteries. After birth the umbilical cord is 

 severed, and thereafter its constituent parts atrophy. Those 

 portions of them which were situated in the umbilical orifice 

 fuse with the margin of the orifice to form the fibrous cicatrix 

 called the umbilicus, and are no longer recognisable as dis- 

 tinct structures ; but the parts which lie within the abdomen 

 are recognisable throughout the whole of life, and will be 

 found enclosed in folds of peritoneum when the abdomen is 

 opened. 



In well -developed subjects a rectus abdominis muscle 

 stands out on each side of the median line, forming a longi- 

 tudinal prominence, which is broader above than below. Its 

 lateral margin, which forms a curved line with the concavity 

 directed medially, corresponds with the linea semilunaris i.e. 

 the line along which the aponeurotic tendon of the internal 

 oblique muscle splits to enclose the rectus abdominis. The 

 linea semilunaris is occasionally selected by the surgeon as the 

 site for incisions through the abdominal wall because of its 

 slight vascularity, but it must not be forgotten that an incision 

 of any length passing through it will necessarily divide one 

 or more of the nerves which supply the rectus abdominis. 



The dissector should note that the lateral margin of the 

 rectus abdominis crosses the lower margin of the thorax at 

 the level of the ninth costal cartilage, and the point of cross- 

 ing, on the right side, indicates the position of the fundus of 

 the gall-bladder. 



After the regions of the linea alba and the linea semi- 

 lunaris have been examined, place the index finger on the 

 upper part of the symphysis pubis, at the lower end of the 

 linea alba, and carry it laterally along the pubic crest to the 

 pubic tubercle. At the pubic tubercle it will enter a linear 

 depression which runs upwards and laterally, at the junction 

 of the abdomen and the thigh, along the line of the inguinal 

 ligament, to the anterior superior spine of the ilium. All the 



