1776 HUMAN ANATOMY. 



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

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



Acquired Umbilical 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 fibrous tissue takes place, and as the abdomen grows, the 

 traction of these cords expresses 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 ijifantile innbilical 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 herniae 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 below the umbilicus they are not uncommon, as the linea alba 

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

 very rare. They are 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 

 intra-abdominal pressure is great enough. 



The linea semilunaris, especially below the level of the umbilicus, is a not 

 uncommon site of ventral herniae. It has been suggested that their position is de- 

 termined by the fold of Douglas (page 522), — the semilunar lower margin of the 

 posterior layer of the internal oblique aponeurosis, which fuses with the transversalis 

 aponeurosis to form the posterior sheath of the rectus muscle, which ends about 

 half-way between the umbilicus and the pubes. Below that all the aponeuroses pass 

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

 muscle separated from the abdominal contents only by the transversalis fascia and 

 peritoneum. 



Ventral hernia of the linea semilunaris near its lowest portion and direct hernia 

 issuing through the internal inguinal fossa (page 1770) are indistinguishable, if not 

 practically identical. 



