I 77 6 HUMAN ANATOMY. 



ment at that point. If this is overlooked and the cord is tied within the limits of 

 thi> enlargement, the intestine, if not previously replaced, may be included. 



Acquired I 'mbilical Hernia. Usually, although the cord is tied at a short dis- 

 tance from the abdominal wall, the stump separates on a level with the latter on 

 account of the contraction of the elastic fibrous tissue around the umbilicus. This 

 cuts off the urachus and the vessels passing through the ring, the two allantoic 

 or hypogastric arteries and the umbilical vein. Viewed from within, the fibrous 

 cords representing these obliterated vessels would be seen converging to the puckered 

 umbilical scar, the vein from above, the urachus and the arteries from below. As 

 the usual contraction of til>n>us tissue- takes place, and as the abdomen grows, the 

 traction of these cords depresses the umbilicus so that anteriorly it lies a little below 

 the surrounding surface of the abdomen. The larger amount of tissue represented 

 by the- urachus and the two arteries and their close attachment to the lower edge 

 cause that portion of the umbilicus to become the stronger, the umbilical vein being less 

 closely connected to the upper edge of the ring. 



In infantile umbilical hernia these changes are not complete, but when a 

 knuckle of gut protrudes through the umbilicus during infancy, as a result of 

 increased intra-abdominal pressure, it usually escapes between the vein and the upper 

 margin of the ring on account of their loose attachment. The coverings are peri- 

 toneum, transversalis fascia, and skin. These herniae are usually small, and are often 

 cured spontaneously by the contraction of the umbilical and periumbilical scar tissue. 

 Their occurrence is favored by tight phimosis or by constipation, causing straining, 

 or by improper feeding, causing flatulence. After infancy umbilical hernia is rare 

 until adult life. 



The umbilical hernia of adults is far more common in women than in men (73 

 per cent), and is especially favored by obesity with accumulation of fat in the 

 omentum and mesentery and by repeated pregnancies. The coverings of such a 

 hernia are peritoneum, transversalis fascia, superficial fascia, the fibrous tissue of the 

 umbilical scar and the linea alba, and skin. 



For the reasons above given, it appears usually at the upper semicircumference 

 of the umbilical ring and often involves the linea alba immediately above it, a form 

 of ventral hernia. Such hernia are very apt to contain omentum the growth of 

 fat in which often makes them irreducible and portions of the colon, and, on 

 account of the readiness with which fecal obstruction may be caused in the large 

 intestine, they are prone to incarceration. 



Ventral herniae protrude through the abdominal parietes at other points than 

 the umbilicus or groin, or than those weakened by the passage of vessels and nerves 

 from within outward. 



The most common are in the linea alba, between the umbilicus and a point 

 midway between it and the ensiform cartilage {epigastric hernia). Above that they 

 are very rare, as the effect of gravity is lacking and the contiguous viscera are less 

 mobile. Immediately In-low tin- umbilicus they are not uncommon, as the linea alba 



till an appreciable width. Lower, where it has become a mere raphe, they are 



very rare. They an often associated with subserous lipomata, and may be caused 



by them. The protrusion of fat from the subserous tissue is thought to draw the 



peritoneum out into a diverticulum which readily becomes a hernial pouch when 



ibdominal pressure is great enough. 



The linea stnii/nn.ins. especially below the level of the umbilicus, is a not 



uncommon site ,,t ventral her.me. It has been suggested that their position is de- 



rmined by the told ,,f Don-las < page 522), the semilunar lower margin of the 



lave, of the internal oblique aponeurosis, which fuses with the transversalis 



apo' rm the posterior sheath of the rectus muscle, which ends about 



twee,, the u.nb.licus and the pubes. Below that all the aponeuroses pass 



the rectus, leaving the posterior surface of the inferior portion of that 



muscle separated tn>m the abdominal contents only by the transversalis fascia and 



peritoneum. 



Ventral hernia ,,f the linea semflunarii near its lowest portion and direct hernia 

 hTOUgh the internal m^ina! fossa (page 1770) are indistinguishable, if not 

 practically identical 



