The two lower intercostal, the subcostal, and the four lumbar arteries, run forward between the transversalis and internal oblique, and anastomose with the internal mammary, deep epigastric, and circumflex iliac, and with one another.

The deep epigastric arises from the external iliac just above Poupart, and to the inside of the internal abdominal ring, and runs upwards and inwards along with its venae comités to pierce the fascia transversalis, and enter the rectus sheath above the fold of Douglas, where it anastomoses with the internal mammary, which anastomosis is of importance in ligature of the common or external iliac.

The deep circumflex iliac arises from the outer side of the external iliac, nearly opposite to the deep epigastric, and, accompanied by its venae comités, runs in a groove between the transversalis and iliac fasciae outwards, just above Poupart's ligament, to the anterior superior spine, where it pierces .the transversalis, and runs back and breaks up, anastomosing with the lower intercostal and lumbar arteries, and the ilio-lumbar of the internal iliac. It should be noted that not merely do these vessels anastomose with one another; but that they also anastomose with the vessels supplying some of the abdominal viscera. Thus, the lower intercostal arteries communicate with the hepatic, renal, and suprarenal arteries, while the lumbar and circumflex iliac vessels anastomose with those supplying the ascending and descending colon.

The umbilicus is the last portion of the abdominal cavity to become closed, and through it, by means of the umbilical cord during foetal life, the embryo receives nourishment and oxygen, from the yolk-sac and blood-supply, while excreted matter passes out along the allantois. In the embryo of three months all the abdomen, save the umbilical ring, has closed, and through this fibrous ring the cord passes. Externally the cord is invested with amnion, which latter becomes continuous with the abdominal wall at the umbilicus, and the structures contained within it are (a) two arteries and one vein. These structures separate at the umbilicus, the arteries running downwards and outwards, one on either side, to become the common iliac trunks, while the vein runs upwards to the liver. In true congenital umbilical hernia the bowel generally passes out between these three structures which are spread over its surface. After birth the two arteries become the obliterated hypogastric arteries, while the vein forms the round ligament of the liver. As the abdomen increases in size, these structures do not tend to grow along with it, and thus the umbilicus is pulled inwards and downwards, carrying the vein along with it, so that in the adult the upper segment of the umbilicus is left free, (b) Up to the third month the midgut is in communication with the yolk-sac, or umbilical vesicle, by the vitello-intestinal duct, the loop of bowel, which is known as the umbilical loop, lying outside the body wall at first. About the third month, however, this communication should disappear, and the bowel retire within the abdomen. Where for any reason the bowel does not retire, a congenital hernia is formed. Sometimes, on the other hand, a portion of the duct may persist. This persistent portion forms what is known as Meckel's diverticulum, which varies in length, and arises from the ileum from 1 to 4 feet from the ileocecal valve. Sometimes the free end of the diverticulum is connected to the umbilicus by a fibrous cord (which is an occasional cause of strangulation), and in other cases the duct remains patent right up to the umbilicus, causing a fcecal fistula. Cystic adenomata occasionally occur about the umbilicus in connection with the remains of the duct, (c) The allantois grows out from the ventral aspect of the hind gut, and when the placenta is formed its vessels convey the blood between the embryo and the placenta. Normally the allantois shrivels, save its lower end, which forms the urinary bladder. A fibrous cord running up in the middle line between the two hypogastric arteries from the apex of the bladder to the umbilicus represents the shrivelled intra-abdominal stalk, which is known as the urachus. Sometimes the urachus remains patent, giving rise to a urinary fistula at the umbilicus. In other cases the urachus becomes obliterated at either extremity, while the central portion becomes distended, forming a cyst of the urachus (d) The cord, as stated above, is covered by a layer of amnion, and, in addition to the structures enumerated, contains a mass of nbro-myxomatous tissue, known as Wharton's jelly.

Three forms of hernia may be met with at the umbilicus. (1) Congenital. This may be associated with some grave defect in the abdominal wall, the viscera remaining exposed, or covered by only a thin membrane. Sometimes the viscera lie outside the abdominal cavity (ectopia or exomphalos). In other cases the abdominal wall may be normal, but a loop of bowel, as already described, may project within the cord for some distance beyond the umbilicus, and thus be liable to ligature with the cord, giving rise to intestinal obstruction. Where such herniae are recognized, and do not easily return to the abdomen, great care must be taken in cutting the parts at the umbilicus to increase the aperture, as important structures practically surround the bowel. (2) A small infantile form of umbilical hernia is not infrequently met with, the condition arising soon after birth from stretching of the umbilicus. It is generally cured by the steady application of pressure for some time. (3) As already stated, the umbilical scar tends to become invaginated and pulled downwards as the patient grows, even the vein arising from the lower border in the adult. Thus, in acquired umbilical hernia the protrusion takes place above these structures, through the upper portion which is comparatively weak and thin. A further possible cause for hernia selecting this upper portion is the occasional presence of an umbilical canal, which is a small median diverticulum of the fascia transversalis, lined by peritoneum, the mouth of which is directed upwards, while the blind extremity is directed toward the upper margin of the umbilicus. Such herniae are generally loculated and thin-walled, the peritoneum being very adherent to the skin.