An introduction to the study of embryology / by Alfred C. Haddon.

  • Haddon, Alfred C. (Alfred Cort), 1855-1940.
Date:
1887
Catalogue details

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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    ]^otalli may unite the second, third, and fourth arches in adult Urodeles. The venous system of Fishes primitively consists of a median unpaired subintestinal vessel extending from the end of the tail to the heart; indeed, the heart may be considered as a specialised portion of this vessel. Later, cardinal veins are developed, as in Embryonic Amniotes, but in Fishes they persist as the main venous trunks. The caudal portion of the subintestinal vessel acquires a secondary connection with the posterior cardinal veins. In some cases this, its anastomosis, breaks up into capillaries in the mesonephros, thus forming a renal portal system. After the appearance of the cardinal veins the main portion of the subintestinal vein disappears, but a remnant of one of its branches occurs in some Elasmobranchs as the vein of the spiral valve, and it also leaves its trace in the hepatic portal system. A branch from the subintestinal goes to the yolk-sac, and the common trunk is imbedded in the developing liver. Later, vessels from the alimentary viscera are developed, which break up in the liver. The hepatic veins convey blood from the liver to the sinus venosus of the heart. In some Fishes vessels from the anterior abdominal wall enter into the portal circulation. These may be regarded as the fore- runners of the paired anterior abdominal veins. The ductus venosus and the caudal vein may be regarded as the representatives of the subintestinal vein in Amniota. In Fishes the air-bladder ranks as an ordinary viscus of the mesenteric series, as its blood enters into the hepatic portal system before being returned to the heart; the only exception occurring is in the Dipnoi, where the pulmonary vein, as it may now be called, carries the blood direct to the left auricle. The same obtains in Amphibia. The Amphibia initiate a new departure in the development of a vena cava inferior, which functionally replaces the larval posterior cardinal veins. The hepatic veins enter into the vena cava inferior. On the disappearance of the posterior cardinals the ductus Cuvieri (superior vense cavse) are connected only with the anterior cardinals (jugular veins). At first two anterior abdominal veins occur, and open anteriorly into the sinus venosus, having previously united with a vein from the truncus arteriosus. An epigastric branch from the iliac vein and veins from the urocyst or bladder (allantois) join them, after