DISEASES OF THE NAVEL At birth the umbilical cord forms the connecting link between the body of the embryo and the placenta. It is a cord, about as thick as the little finger, twisted in many spirals and consists fundamentally of the jelly of Wharton, an embryonic mucous tissue which contains countless connective tissue and elastic fibres embedded in its colloid matrix. The cord is covered with amnion throughout its length; this terminates abruptly about 1 cm. above the fetal abdominal wall, leaving the proximal portion covered with skin. The umbilical cord contains no capillaries; only at its point of entrance into the navel does there appear, in the peritoneal tissue, a rich capillary network, whose branches extend on to the intra-abdoininal portion of the umbilical vessels and send numerous twigs upward into the collar of skin cover ing the lowest portion of the cord; here, at the boundary between amnion and skin, they form a vascular circle (Byrd).
At birth the umbilical cord contains: 1. The two umbilical arteries which conduct the blood from the foetal body to the placenta. They extend to the navel on either side from the common iliac artery; they are thick walled vessels and like the umbilical cord. are wound in spirals.
2. The umbilical vein which conducts the blood from the placenta to the inferior vena cava. It passes through the cord to the body of the child, thence through the navel ring along the abdominal wall to the left branch of the portal vein which conducts the placental blood through the duct us venosus Arantii into the inferior vena cava of the foqus.
3. Strands and epithelial remains representing a portion of the chictus am pholom (wider ic us (the vitelline duct), which disappears at the first mouth of foetal life.
4. Clumps of cells arising from the involuted allantoic duct. The extra-abdominal portion of the allantois undergoes retrograde meta morphosis in the first weeks of foetal life; leaving only a few epithelial clumps, whereas the abdominal portion remains as the urachus; it is normally a solid strand or often partially or totally patent and lined with epithelium and after birth becomes the ligament.
Immediately after birth, usually after the cessation of pulsations in the umbilical arteries, the cord is cut; among civilized peoples, after previous ligature. There remains adhering to the body of the child a portion of the cord, one or more centimetres in length, which under goes mummification during the first days of life. On the fourth to ninth day, rarely earlier or later, it separates from its attachment with a slight inflammatory reaction. The separation occurs later with thick edem atous cords and in premature children than with thin cords and strong children. The skin of the abdominal wall which covers the beginning of the cord for a distance of cm., rolls in at the same time and thus forms the umbilical fold, the upper half of which is smaller than the lower. The navel fold usually hides the base of the navel so com pletely that one is unable to see its epidermization without separating the folds. The healing of the navel wound progresses, with scant secre tion, by epidermization from the periphery toward the centre.
The healing of the navel wound and its pathological disturbances depend closely on the peculiar construction of the umbilical vessels. The umbilical arteries differ materially in structure from the other ves sels of the body. They possess a single layer of endothelium and a highly developed musculature. The latter is arranged in two layers. The inner layer is composed of longitudinally disposed fibres richly mingled with elastic fibres and connective tissue. The outer layer is still thicker, con tains principally circular fibres and is poor in elastic substance and connective tissue; occasionally besides the circular fibres it contains some longitudinal fibres. Further, the umbilical arteries are enveloped in a dense mantle of embryonic connective tissue; this forms the ad ventitia of the arteries and accompanies them downwards through the navel ring into the abdominal cavity as far as the summit of the bladder.