640 A MANUAL OF ANATOMY 



In young persons the upper part of the bladder, being extra- 

 pelvic, lies behind the lowest part of the linea alba. In adults 

 the upper part of that viscus, when abnormally distended, also 

 lies behind the lowest part of this line. 



The umbilicus takes the form of a cicatricial depression which 

 is situated in the linea alba at the junction of the upper three- 

 fifths and lower two-fifths. As seen from before it is irregu- 

 larly circular, the skin being more or less puckered according to the 

 state of distension of the abdomen. When viewed from behind it 

 is smaller in size, and its long measurement lies transversely. 

 Besides cicatricial tissue and fat, the lower part of it contains the 

 upper ends of the urachus and obliterated hypogastric arteries, 

 whilst the upper part is occupied by part of the obliterated runbilical 

 vein. The upper part is weaker than the lower. The umbilicus 

 is on the same horizonal plane as the disc between the bodies of 

 the third and fourth lumbar vertebrae. 



During intra-uterine life the umbilicus is an opening by which 

 the hypogastric arteries leave the abdomen of the foetus on their 

 way to the placenta, and by which the umbilical vein, on its way 

 from the placenta, enters the abdomen. A few days after birth, 

 however, the opening becomes permanently closed. 



The linese semilunares coincide with the outer borders of the 

 recti abdominis. The position of each is indicated by a line drawn 

 from the lowest part of the eighth costal cartilage to the pubic 

 spine. This line is curved, with the convexity outwards, and at the 

 level of the umbilicus it is about 3 inches from it. Over the upper 

 three-fourths of the rectus abdominis it indicates the splitting of 

 the aponeurosis of the internal oblique into two laminae, which 

 encase that extent of the muscle in a sheath. Over the lower fourth 

 it indicates where the aponeuroses of the external oblique and 

 internal oblique and the anterior aponeurosis of the transversalis 

 abdominis pass in front of the rectus. 



The linese transversae are usually three in number, on either 

 side. They are tendinous intersections or inscriptions which cross 

 the rectus in the following situations : one at the level of the 

 umbilicus, one at the level of the lower part of the ensiform process 

 of the sternum, and one about midway between these two. The 

 positions of the linege transversae are indicated by three faint 

 grooves. The anterior wall of the sheath of the rectus is closely 

 bound down to the tendinous intersections, and so each muscle 

 above the level of the umbilicus is mapped out into two quadrangular 

 areas, and the interior of the sheath, anterior to the muscle, is also 

 divided into two distinct compartments. An abscess may form in 

 one or other of these compartments, or there may be a spasmodic 

 contraction of one or other of these quadrangular areas of the 

 muscle, a condition in each case which would necessarily have a 

 circumscribed limit, and might lead to error in diagnosing affections 

 really having their seat within the abdominal cavity. 



The spino-umbillcal lines are two in number, right and left, 



