An introduction to the study of embryology / by Alfred C. Haddon.
- Haddon, Alfred C. (Alfred Cort), 1855-1940.
- Date:
- 1887
Licence: Public Domain Mark
Credit: An introduction to the study of embryology / by Alfred C. Haddon. Source: Wellcome Collection.
Provider: This material has been provided by University of Bristol Library. The original may be consulted at University of Bristol Library.
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![which they unite into a single vessel. The atrophy of the right vein is said to result in a single anterior abdominal vein. A secondary connection occurs between the anterior abdominal and the portal system, which persists in the adult. In other respects the Amphibia are essentially piscine in their vascular system. Summary of the History of the Aortic Arches.—As there is still some uncertainty concerning the fate of some of the aortic arches in the various groups of Vertebratep, it may not be superfluous to briefly recapitulate the facts as at present known. In this summary, as in the foregoing account, the view is adopted which is most gene- rally current, viz., that there is one prehyoid aortic arch, usually termed the mandi- bular or first aortic arch, the hyoid is the second, while in most Fishes there are four branchial aortic arches. Dohrn terms the aortic arch immediately in front of the hyoid the arteria thyreoidea mandibularis, or shortly the thyroid artery (the mandibu- lar of Balfour), which, in Elasmobranchs, after receiviug a venous commissure from the hyoid arch, is called the spiracular artery, as it supplies the spiracle. First aortic arch (mandibular ?), present in all embryonic Vertebrata, except the Amphibia, only persisting in Elasmobranchii, and that imperfectly, as the spiracular artery. Second aortic arch (hyoid), present in all embryonic Vertebrata, but imperfect in larval Amphibia. Persistent in Elasmobranchii, usually so in Ganoidei, rudi- mentary in Teleostei (as artery of pseudobranch), may disappear in some Dipnoi, and partially persists as the lingual artery in Amphibia and Amniota. Third aortic arch (first branchial), present in all larval forms, and persists as a complete arch in all Fishes. In adult Amphibia and Amniota it loses its con- nection with the other arches and gives rise to the common carotid trunks. Fourth aortic arch (second branchial), retains its connection with the dorsal aorta throughout the Vertebrate series. Fifth aortic arch (third branchial), persists in all adult Fishes, and to a diminished degree in adult Urodela (still uniting with the dorsal aorta), is lost during the metamorphosis of Anura [Boas], and disappears in the Amniota. Sixth aortic arch (fourth branchial), persists throughout the Vertebrate series. In some Ganoidei (Polypterus, Amia) and Dipnoi also giving a branch to the air- bladder, and in adult Amphibia and Amniota supplying the lungs. In adult Urodela alone is a connection still left with the dorsal aorta, and in Anura a large cutaneous branch is given off. It is usually stated that the pulmonary artery of Anura and Amniota is the third branchial aortic arch, and that the fourth disappears. The subject requires reinves- tigation, as probably there is a fusion of these two arches, both of them losing their connection with the dorsal aorta, but the fourth branchial still giving origin to the pulmonary artery. Boas has shown that this is actually the case in the young Frog, and in Salamandra the third branchial arch has the appearance of a diminishing artery. It is, moreover, very improbable that the arterial supply of the lungs should shift from the last arch to the one in front of it. If this be admitted, the term fifth aortic arch in the above description of the development of the arterial arches in Amniota must be understood as implying fifth + sixth aortic arch, making seven arches in all. Changes Undergone in the Circulation of Foetal Mammals.—The earliest phases in the circulation have already been described. Later all the venous blood passes directly into the right auricle. The venous blood from the head and upper portion of the body is returned by the two venae cavse superiorcs (innominate veins). In most Mammals the proximal portion of the left superior vena cava atrophies ; so all](https://iiif.wellcomecollection.org/image/b21443919_0269.jp2/full/800%2C/0/default.jpg)
