. Hand-book of physiology . alli) rapidly becomes narrowed, and in thecourse of the first few weeks after birth its cavity is entirelyobliterated: the anterior portion becomes the trunk of the 694 DEVEL0P3IEXT OF VEINS. Fij. 98.* independent arterias tlie same time the closureof tlie foramen ovale takesplace. Veins.—The conformation ofthe venous system also is at firstthe same in the embrjoes of allvertebrate animals, and subse-quently departs, in various ways,from the common primitive the original condition thereare two anterior venous trunks(the jugular veins), and two
. Hand-book of physiology . alli) rapidly becomes narrowed, and in thecourse of the first few weeks after birth its cavity is entirelyobliterated: the anterior portion becomes the trunk of the 694 DEVEL0P3IEXT OF VEINS. Fij. 98.* independent arterias tlie same time the closureof tlie foramen ovale takesplace. Veins.—The conformation ofthe venous system also is at firstthe same in the embrjoes of allvertebrate animals, and subse-quently departs, in various ways,from the common primitive the original condition thereare two anterior venous trunks(the jugular veins), and two pos-terior trunks, the cardinal veins. One of the anterior trunks, andone of the posterior, unite on each side and form a transversecanal,—the ductus Cuvieri. The two ductus Cuvieri unitebeneath the oesophagus to form a shorter main canal whichenters the aimcle,—at that time a simple cavity. The cardi-nal veins are originally formed by the caudal veins, branchesfrom the kidneys and Wolffian bodies, and others from the. * Fig. 98. Plan of the transformation of the system of aortic ai-chesinto tlie permanent arterial trunks in mammiferous animals; after VonBaer. 1. Situation of the original single trunk which arose from thesingle ventricle, and which has become divided into two tubes: it gaveoflf five pairs of aortic arches, which terminated in the two roots of theaorta (2, 2). Those of the arches which are obliterated at a very earlyperiod are marked by dotted lines. The first arch of the right side vdihthe root of the aorta of that side (2) which remains longer, and formsthe right ductus arteriosus, is drawn as a very narrow vessel, with adotted line on each side. The vessels which still exist at birth aredrawn of the full size. These are the first arch of the left side, consti-tuting the ductus arteriosus Botalli, which is in greater part obUteratedsoon after birth, and the second arch of the left side, constituting the per-manent arch of the aorta (3). The subclavian ar
Size: 1135px × 2202px
Photo credit: © Reading Room 2020 / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1850, booksubjectphysiology, bookyear1
