For the purpose of fixing the main facts in connection with the development of the higher mammalian hepatic circulation, and in order to obtain a demonstration of the cycle through which the different veins pass, the student is recommended to examine, preferably by personal dissection, a limited series of lower vertebrates which can be readily procured and easily injected. The following series has been selected, but it will be understood that other forms can be substituted, according to the local conditions which govern the supply of the material. 1. _Fish._ _A Selachian_, the common skate (_Raja ocellata_) or dog-fish (_Acanthias vulgaris_). 2. _Amphibian._ (_a_) Urodele. _Necturus maculatus._ (_b_) Anura. The common _frog_. 3. _Reptile._ Preferably, on account of the ease of injection, one of the larger lizards, as _Iguana tuberculata_. The turtles, although somewhat more difficult objects to prepare, can be substituted. 4. _Bird._ The common fowl. 5. Human foetus at term. =1. Fish.=--The venous system can be injected by tying a canula in the lateral vein, and injecting both cephalad and caudad, or by injecting cephalad through the caudal vein. The injection of the systemic veins can also be made caudad through one of the ducts of Cuvier, combined with an injection cephalad of the caudal vein. [Illustration: FIG. 262.--Diagram of the veins of a selachian. (Wiedersheim, after Parker.) The lateral vein arises from a venous network surrounding the cloaca, receiving one or more cutaneous veins of the tail, veins of the body-wall, and veins of the pelvic fins. The caudal vein divides at the posterior end of the kidney into the two renal-portal veins, from which the advehent veins of the renal-portal system are derived. The revehent renal-portal veins join to form the posterior cardinal veins, which, after dilating enormously to form the cardinal sinuses, join with the anterior jugular, subclavian, and lateral veins to form the ducts of Cuvier. The latter receive the inferior jugular veins, from the deep parts of the head and neck and the terminations of the hepatic portal system (hepatic sinus). The hepatic portal vein is formed by the veins of the oesophagus, stomach, and intestines. After traversing the capillary vessels of the liver, the revehent hepatic veins unite to form an extensive hepatic sinus before entering the heart.] The following main facts are to be noted in the venous system of the Selachian (Fig. 262): =1. There are Two Portal Systems.= (_a_) _Renal Portal System._--The caudal vein divides near the vent into two branches which course along the lateral border of the kidneys, sending _afferent_ or _advehent_ veins into the organ. The blood traverses the renal capillaries and is gathered together by the _efferent_ or _revehent_ veins, which empty into median paired vessels, the posterior cardinals.