The development of the human body; a manual of human embryology . l division of the aortic bulb occurs, theseptum is so arranged as to place the sixth arch in commu-nication with the right ventricle and the remaining vesselsin connection with the left ventricle, the only direct com-munication between the systemic and pulmonary vessels / THE ARTERIES. 265 being by way of the ductus arteriosus, whose significancewill be explained later (p. 290). One other change is still necessary before the ves-sels acquire the ar-rangement which theypossess during fetallife, and this consistsin the disappearan
The development of the human body; a manual of human embryology . l division of the aortic bulb occurs, theseptum is so arranged as to place the sixth arch in commu-nication with the right ventricle and the remaining vesselsin connection with the left ventricle, the only direct com-munication between the systemic and pulmonary vessels / THE ARTERIES. 265 being by way of the ductus arteriosus, whose significancewill be explained later (p. 290). One other change is still necessary before the ves-sels acquire the ar-rangement which theypossess during fetallife, and this consistsin the disappearanceof the lower portionof the right aortic arch(Fig. 139), so that theleft arch alone formsthe connection be-tween the heart andthe dorsal aorta. Theupper part of the rightaortic arch persists toform the proximalpart of the right sub-clavian artery, theportion of the ventraltrunk which unites thearch with the aorticbulb becoming thebrachio-cephalic (in-nominate) artery. From the entirelength of the thoracicaorta, and in theembryo from the aor-tic arches, lateral. Fig. 139.—Diagram Illustrating theChanges in the Arrangement of theBranchial Arch Vessels. The broken lines indicate portions of theoriginal vessels which have , Aorta; A A, aortic arch; DA, ductusarteriosus; EC, external carotid; IC,internal carotid; IM, internal maxillary;L, lingual; P, pulmonary artery; PA,pulmonary aorta; SA, systemic aorta;Sc, subclavian; I to VI, original branchialarch vessels. branches arise corresponding to each segment and ac-companying the segmental nerves. The first of thesebranches arises just below the point of union of the ves- 266 THE DEVELOPMENT OF THE HUMAN BODY. sel of the sixth arch with the dorsal trunk and accom-panies the hypoglossal nerve (Fig. 140, h), and thatwhich accompanies the seventh cervical nerve arises just above the point of unionof the two aortic arches(Fig. 140, s), and extendsout into the limb bud,forming the subclavianartery.* Further down twelvepairs
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectembryol, bookyear1902
