. Text-book of embryology. Embryology. VI AETEEIAL SYSTEM 401 conus and its derivatives, with the right side of the veutricular cavity in proximity to the opening of the pulmonary artery. With the separation of the two ventricles the arch in question remains connected with the right ventricle. With increasing efficiency of the pulmonary circulation the venous blood of the right ventricle would be drawn off more and more to the pulmonary artery and, correlated with this, we find in those Sauropsida in which metabolism is most active and respiration most efficient that this fourth arch on the le
. Text-book of embryology. Embryology. VI AETEEIAL SYSTEM 401 conus and its derivatives, with the right side of the veutricular cavity in proximity to the opening of the pulmonary artery. With the separation of the two ventricles the arch in question remains connected with the right ventricle. With increasing efficiency of the pulmonary circulation the venous blood of the right ventricle would be drawn off more and more to the pulmonary artery and, correlated with this, we find in those Sauropsida in which metabolism is most active and respiration most efficient that this fourth arch on the left side with its aortic root disappears completely during development, leaving only the single right-hand arch and n m Fn;. 189.—Blood-vessels of Crocodile of stage 55-56. (After Hochstetter, 19 Arteries are shown in outline, veins black. c, anterior cardinal vein ; , aortic root; &.a, basilar artery; , dorsal carotid ; ot, otocyst; , posterior cardinal vein ; , right pulmonary artery \ , ventral carotid ; III-VT, aortic arches. root to form the proximal part of the systemic aorta (Birds, Fig. 187a, D). Arch V, in the Amniota, appears only transiently and so greatly reduced in size as to have completely escaped the notice of the earlier investigators. Hence in Eathke's classical scheme of the aortic arches which is given in the older text-books only five arches are shown, the posterior one being called the fifth. With our present-day knowledge of .the homology of the lungs of Amniota with those of Crossopterygians and Lung-fishes, such a scheme is clearly erroneous, as it would involve the pulmonary artery, which is certainly the same vessel throughout, taking its origin in the Amniotes from the fifth and in the Ichthyopsida from the sixth aortic arch. So without any special embryological data we should VOL. ii 2d. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - colora
Size: 1799px × 1389px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, bookpubli, booksubjectembryology
