. Elements of Comparative Anatomy. veins of tteir own side. In many Teleostei, tliis caudal vein is continued into the riglit cardinal by a large, and into the left cardinal by a smaller branch; in this case the left cardinal vein is also smaller than the right one. This leads to the condition in which the whole of the caudal vein passes into the right cardinal j this has been observed in a number of Teleosteaus. As the caudal vein sends off branches into the kidneys, which either break up completely or partially in. this organ, these branches form the venffi renales advehentes, and send their
. Elements of Comparative Anatomy. veins of tteir own side. In many Teleostei, tliis caudal vein is continued into the riglit cardinal by a large, and into the left cardinal by a smaller branch; in this case the left cardinal vein is also smaller than the right one. This leads to the condition in which the whole of the caudal vein passes into the right cardinal j this has been observed in a number of Teleosteaus. As the caudal vein sends off branches into the kidneys, which either break up completely or partially in. this organ, these branches form the venffi renales advehentes, and send their blood into the cardinal veins through the venae reve- hentes. In this way the renal portal system is developed. A second vascular apparatus of similar character has its roots on the digestive canal; its venous blood is carried to the liver by a trunk which is known as the portal vein. It is distributed in this organ, and is carried to the common venous sinus by hepatic veins, which are generally united into several trunks. In this arrangement of the venous system in Fishes we may distinguish the paired, and ordinarily symmetrical, portion from the unpaired portion, which is solely represented by the hepatic veins. We will first follow out the former in its changes throughout the Vertebrate series, for in all of them its essential characters, at any rate, may be observed in the early stages of development, as a transmitted arrangement, and, since it is the groundwork of the embry- onic venous system, it furnishes the starting- point for all later metamorphoses. Fig. 334. Diagram of the primitive venous system. j Jugular, c Cardinal vein. dc Ductus Cuvieri. h Venso hepaticse. sv Sinus 438. Kg. 335. Anterior per. tion of the venous sys- tem of an embryonic Ophidian, i) Ventricle. ha Bulbus arteriosus, c Auricle. DC Ductus Cuvieri. vc Cardinal vein, vj Jugular. ^'M Um- bilical vein. U Primitive kidney. I Rudiment of the labyrinth (after H. Eathke). • In the Amphibia an
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