THE ABDOMEN. 



37 1 



Lines, or Lineae. There are certain lines on the abdomen, called linea alba, 

 HnecB semilunares, linece transverse, and sometimes there are present linefs albicantes. 



Linea Alba. The linea alba passes in the median line from the ensiform 

 cartilage to the symphysis pubis. It is formed by the fusion of the sheaths of the 

 recti muscles. A little over half way down is the umbilicus. 



The linea alba is broad and distinct above the umbilicus, separating the recti 

 muscles a half centimetre ( \ in. ) or more ; below, it diminishes and almost or quite 

 disappears, leaving the recti muscles almost in contact with each other. Its fibres 

 run longitudinally, obliquely, and transversely. The transverse fibres are the 

 strongest and not infrequently have gaps between them which allow the subperitoneal 

 fat to protrude and form a hernia in the median line which can be felt under the skin 

 as a small, firm, rounded body. When these hernias are operated on they are found 

 to be masses of subperitoneal fat with a somewhat constricted pedicle which emerges 



PIG. 385. Surface anatomy of the abdomen; lines and regions. 



from a transverse slit in the linea alba. The peritoneum is not protruded. Some of 

 the fibres of the linea alba are prolonged into the subcutaneous tissue and skin, thus 

 binding it down and forming a groove distinctly visible above the umbilicus but dis- 

 appearing below it. It does not long prevent extravasated urine from passing 

 from one side to the other (Fig. 385). 



The Umbilicus. The umbilicus lies over the disk between the third and fourth 

 lumbar vertebrae, and 2.5 to 4 cm. (i to i^ in.) above a line joining the tops of the 

 crests of the ilia. In the fcetus it transmits the umbilical vein, the two umbilical 

 arteries, and the remains of the vitelline duct and stalk of the allantois. The 

 umbilical vein becomes the round ligament of the liver and is the only structure 

 passing into the upper half of the umbilicus. The umbilical arteries within the body 

 form the obliterated hypogastric arteries, being continuous with the superior vesicals. 

 The vitelline duct in fetal life passes from the umbilical vesicle to the small intestine. 



