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 fœtus 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.
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.