The development of the human body; a manual of human embryology . ble fromtheir adult arrangement. Theearliest representative of them isthe superior mesenteric artery,whose origin from the left om-phalo-mesenteric has alreadybeen described. Several othervisceral branches occur both inthe thoracic and abdominal re-gions, but they are irregular intheir distribution, the unpairedbranches of the abdominal re-gion having probably condensedfrom an original segmental con-dition to form compound trunkssuch as the cceliac axis and theinferior mesenteric. One pair of the visceralbranches, the umbilical
The development of the human body; a manual of human embryology . ble fromtheir adult arrangement. Theearliest representative of them isthe superior mesenteric artery,whose origin from the left om-phalo-mesenteric has alreadybeen described. Several othervisceral branches occur both inthe thoracic and abdominal re-gions, but they are irregular intheir distribution, the unpairedbranches of the abdominal re-gion having probably condensedfrom an original segmental con-dition to form compound trunkssuch as the cceliac axis and theinferior mesenteric. One pair of the visceralbranches, the umbilical arteries,require more than a passingnotice on account of their em-bryonic importance. They are formed at a very earlystage and arise by a short common trunk from the anteriorsurface of the aorta (Fig. 141, U1). They pass directlyforward on the medial side of the Wolffian duct (see p. 361)to the terminal portion of the intestine, and thence passout along the sides of the allantois to the chorionic there are formed from the aorta just below the origin. Fig. 141.—Diagram Illus-trating the Developmentof the Umbilical Arter-ies. A, Aorta; CI I, common iliac;Ell, external iliac; III, in-ternal iliac; V, umbilicalartery; Ul, the primaryproximal and £/2,the secon-dary proximal part of theumbilical ; vid, Wolffianduct. 268 THE DEVELOPMENT OF THE HUMAN BODY. of the umbilicals, the lateral branches () which be-come the common iliacs, and from each of these a shortbranch (U2) arises which passes to the outer side of theWolffian duct and unites with the umbilical arteries,whereupon the original proximal portions of these arteriesdisappear and they come to arise from the iliacs instead ofdirectly from the aorta. At birth the portions of the arte-ries beyond the umbilicus are severed when the umbilicalcord is cut, and their intra-embryonic portions, whichhave been called the hypogastric arteries, quickly undergoa reduction in size. The proximal portion of the allantoispersi
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectembryol, bookyear1902
