Fig. 264.—Dissection of veins of Necturus maculatus, mud-puppy. (Columbia University Museum, No. 1835.)
The postcava has been divided at the cephalic end of the liver just before entering the sinus venosus, and the postcardinals have been cut prior to their junction with the subclavian veins.
The stomach has been turned caudad. The abdominal vein has been divided after the common trunk has been formed by branches from the iliac veins. The latter are seen entering the afferent renal-portal vein, derived from the bifurcation of the caudal vein, along the lateral border of the kidneys.
The junction of the main trunk of the abdominal vein with the hepatic portal vein takes place close to the liver under cover of the pancreas. A series of accessory portal veins continuous with the abdominal vein enter the ventral surface of the liver between the layers of the ventral mesogastrium. The inter-renal segment of the postcava receives the revehent renal-portal veins. The iliac vein enters the advehent renal-portal veins derived from the caudal vein.
Fig. 265.—Venous system of Rana esculenta, frog. (Ecker.)
3. The lateral veins, which we can, as stated, regard for purposes of illustration, without prejudging their genetic significance, as representing the mammalian embryonic umbilical veins, still present the condition corresponding to the early mammalian embryonal stage shown in [Fig. 250]. They are veins of the body walls, emptying cephalad of the liver, directly into the ducts of Cuvier, and through them into the sinus venosus of the heart.
[Fig. 262] shows the arrangement of the venous system in a typical selachian diagrammatically.
2. Amphibian. (a) Urodele.—The following points are to be noted in comparison with the preceding form: