a. The hepatic veins (Venae hepaticae), (Fig. 164 v.h.) are two in number, one from either side of the liver; they open into the posterior caval vein near the Sinus venosus.

b. The renal veins (Venae renales or Venae revehentes), (Fig. 163 r) are four or five small vessels on each side; they pass from the inner border of the kidney inwards and forwards, to form, by their union, the posterior caval vein. The most anterior receive branches from the fat-bodies (see kidney).

c. The spermatic or ovarian veins are four or five in number on each side; they open into the posterior caval vein between the renal veins.

3. The Portal Systems.

[There are, in the frog, two portal systems; the renal and the hepatic. Each of these receives vessels which are derived, directly or indirectly, from the veins of the hinder extremity.

The femoral vein on entering the pelvis divides to form two branches; an iliac vein placed dorsally, and a pelvic vein placed ventrally; the two pelvic veins converge to the middle line of ventral wall of the abdomen, where they unite to form the anterior abdominal vein.]

a. The renal portal vein (Vena renalis advehens princeps), (Fig. 163 a). This vein is formed by the union of the sciatic and the iliac veins; it courses forwards to the outer border of the kidney, and is distributed, by numerous branches, to that organ, chiefly on its dorsal surface. It receives the following veins:‍—

(1) The iliac vein (Vena iliaca externa); this is the dorsal branch formed by the bifurcation of the femoral vein.

(2) The sciatic vein (Vena ischiadica), (Figs. 163 and 165 i) arises at the popliteal space, courses upwards in company with the sciatic nerve between the M. semitendinosus and the M. biceps, then passes, still with the nerve, between the M. vastus externus and the M. pyramidalis into the pelvis. It continues forwards to join the iliac vein. At the root of the thigh this vein communicates with the femoral vein by the Ramus communicans iliacus.

(3) The dorso-lumbar vein (Vena dorso-lumbalis), (Fig. 163 a′) is a vein (or more usually several) arising by twigs in the dorsal and outer walls of the abdomen; it joins the renal portal vein opposite the kidney.

(4) The oviducal veins (Fig. 163 ov) are irregular veins from the oviducts, which open either into the dorso-lumbar vein, or into the renal portal vein.

b. The hepatic portal system.

The liver receives blood from two sources: (1) from the hind-limbs by means of the anterior abdominal vein, and (2) from the alimentary canal by the hepatic portal vein.

The anterior abdominal vein (Vena abdominalis), (Figs. 159 ab, 164 Va) is formed, a little in front of the symphysis pubis, by the union of the two pelvic veins. It courses forwards along the middle line of the ventral body-wall until opposite the liver, where it ascends and divides into three branches, of which two enter the right and left lobes of the liver respectively. The third, the Ramus descendens, joins the hepatic portal vein. The anterior abdominal vein receives the following veins:‍—

α. The vesical vein (Vena vesicalis), (Fig. 163 Vv); a median vein arising in the groove between the lobes of the bladder from lateral branches, which extend outwards on the bladder. This vein communicates above with other vesical twigs which open into the haemorrhoidal vein.

β. Parietal veins, which join the anterior abdominal vein in its course along the ventral body-wall.

γ. A cardiac vein (Vena cardiaca), (Figs. 142, 159 vc, 164 c), which joins the anterior abdominal vein just before its division (see p. 222).

The hepatic portal vein (Vena portarum), (Figs. 159, 164 P) is formed by the union of the gastric, intestinal, splenic, and one of the haemorrhoidal veins. The large vein so constituted passes forwards towards the liver, receives the Ramus descendens from the anterior abdominal vein, and then passes into the left lobe of the liver. Its branches are the following:‍—

(1) The gastric veins. The stomach has three veins:‍—

α. [The Vena coronaria ventriculi, which receives blood from the hinder end of the oesophagus and anterior portion of the stomach.

β and γ. Two other veins which form an Arcus coronarius on the concave surface of the stomach; the hinder receiving in addition the small Venae pancreaticae and the Vena duodenalis; the trunk so formed receives the Vena coronaria ventriculi (Hoffmann).

(2) The intestinal veins; the veins of that portion of the alimentary canal between the middle of the duodenum and the anterior end of the large intestine open into a common vein which joins the hepatic portal vein.

(3) The splenic vein joins either the hepatic portal vein or one of the intestinal veins.

(4) The haemorrhoidal veins are three in number; the anterior opens into the splenic vein, the remaining two into the portal veins through the agency of the intestinal veins.]

4. The Veins of the Hinder Extremity.

The hinder extremity has two venous trunks, the sciatic vein and the femoral vein.

a. The femoral vein (Vena femoralis), (Fig. 165 f) is the larger venous trunk of the hinder extremity. It arises in the popliteal space as a direct continuation of the posterior tibial vein, courses upwards in company with the sciatic artery and nerve, then leaves these to wind forwards and outwards, and appears between the origins of the M. vastus externus and of the M. rectus anterior. The vein here gives off the Ramus communicans iliacus to the sciatic vein, and turns forwards and downwards around the M. glutaeus maximus to reach the floor of the pelvis, near the femoral artery. The vein then bifurcates to form the pelvic and iliac veins.

(1) The Ramus communicans iliacus (Fig. 165 c.i.) forms a communication with the sciatic at the base of the thigh.

(2) The posterior tibial vein (Vena tibialis postica), of which the femoral is a continuation, arises on the dorsal surface of the toes and foot. It runs superficially on the M. extensor longus digiti primi over the ankle-joint, courses upwards and winds round the outer surface of the tibio-fibula to the flexor surface. It receives, in its course, muscular branches, and at the knee a large cutaneous branch.

b. The sciatic vein: this vein has already been described (see p. 247), but the vein from which it arises requires description.

The anterior tibial vein (Vena tibialis antica) arises on the dorsum of the foot by twigs from the toes; it courses under the M. extensor longus digiti primi, then upwards on the anterior surface of the leg, and enters the canal in the tibio-fibula to appear on its hinder surface. The vein then receives twigs from the M. peroneus, the M. tibialis posticus, the M. gastrocnemius, and a large cutaneous branch.

α. The Vena cutanea cruris medialis (Fig. 165 i′) receives branches from both above and below, and enters the popliteal space to join the anterior tibial vein.

β. The anastomosis on the dorsum of the foot, from which the anterior tibial vein arises, receives perforating twigs from the plantar surface.