. The development of the human body : a manual of human embryology. Embryology; Embryo, Non-Mammalian. DEVELOPMENT OF THE ARTERIAL SYSTEM 247 opposite the twelfth thoracic and the inferior mesenteric opposite the third lumbar segment. The umbilical arteries of the embryo seem at first to be the direct continuations of the dorsal aortas (Fig. 146), but as development proceeds they come to arise from the aorta opposite the third lumbar segment, where they are in line with the lateral visceral segmental branches. They pass ventral to the Wolffian duct (see p. 339) and are continued out along with
. The development of the human body : a manual of human embryology. Embryology; Embryo, Non-Mammalian. DEVELOPMENT OF THE ARTERIAL SYSTEM 247 opposite the twelfth thoracic and the inferior mesenteric opposite the third lumbar segment. The umbilical arteries of the embryo seem at first to be the direct continuations of the dorsal aortas (Fig. 146), but as development proceeds they come to arise from the aorta opposite the third lumbar segment, where they are in line with the lateral visceral segmental branches. They pass ventral to the Wolffian duct (see p. 339) and are continued out along with the allantois to the chorionic villi. Later this original stem is joined, not far from its origin, by what ap- pears to be the lateral somatic branch of the fifth lumbar seg- ment, whereupon the proximal part of the original umbilical vessel degenerates and the um- bilical comes to arise from the somatic branch, which is the common iliac artery of adult anatomy (Fig. 152). Hence it is that this vessel in the adult gives origin both to branches such as the external iliac, the gluteal, the sciatic and the in- ternal pudendal, which are distributed to the body walls or their derivatives, and to others, such as the vesical, inferior haemor- rhoidal and uterine, which are distributed to the pelvic viscera. At birth the portions of the umbilical arteries beyond the umbilicus are severed when the umbilical cord is cut, and their intra-embryonic portions, which have been called the hypogastric arteries, quickly undergo a reduction in size. Their proximal portions remain functional as the superior vesical arteries, carrying blood to the urinary bladder, but the portions which intervene between the. Fig. 152.—Diagram Illustrating the Development of the Umbilical Arteries. A, Aorta; CIl, common iliac; Ell, exter- nal iliac; G, gluteal; III, internal iliac; IP, internal pudic; IV, inferior vesical; Sc, scia- tic; U, umbilical; U', primary proximal por- tion of the umbilical; wd, Wolffia
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Keywords: ., bookautho, bookcentury1900, bookdecade1910, booksubjectembryology
