. The development of the human body : a manual of human embryology. Embryology; Embryo, Non-Mammalian. 244 DEVELOPMENT OF THE ARTERIAL SYSTEM until after birth, forming the ductus arteriosus {ductus Botalli) (Fig. 149). When the longitudinal division of the aortic bulb occurs (p. 236), the septum is so arranged as to place the sixth arch in communication with the right ventricle and the remaining vessels in connection with the left ventricle, the only direct communication between the systemic and ec pulmonary vessels being by way of the ductus arteriosus, whose significance will be ex- plained
. The development of the human body : a manual of human embryology. Embryology; Embryo, Non-Mammalian. 244 DEVELOPMENT OF THE ARTERIAL SYSTEM until after birth, forming the ductus arteriosus {ductus Botalli) (Fig. 149). When the longitudinal division of the aortic bulb occurs (p. 236), the septum is so arranged as to place the sixth arch in communication with the right ventricle and the remaining vessels in connection with the left ventricle, the only direct communication between the systemic and ec pulmonary vessels being by way of the ductus arteriosus, whose significance will be ex- plained later (p. 267). One other change is still necessary before the vessels acquire the arrangement which they possess during fetal life, and this consists in the disappearance of the lower portion of the right aortic arch (Fig. 149), so that the left arch alone forms the connection between the heart and the dorsal aorta. The upper part of the right aortic arch persists to form the prox- imal part of the right sub- clavian artery, the portion of the ventral trunk which unites the arch with the aortic bulb becoming the innominate artery. From the entire length of the thoracic aorta, and in the embryo from the aortic arches, lateral branches arise corresponding to each segment and accompanying the segmental nerves. The first of these branches arises just below the point of union of the vessel of the sixth arch with the dorsal trunk and accompanies the hypo- glossal nerve (Fig. 150, h), and that which accompanies the seventh. Fig. 149.—Diagram Illustrating the changes in the branchial arch vessels. a, Aorta; da, ductus arteriosus; ec, external carotid; ic, internal carotid; pa, pulmonary ar- tery; sc, subclavian; I-VI, aortic arch Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original McMurrich, J. Playfair (J
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