Turn the Platana over again on to its back and note the renal portal vein from the ventral side. Joining the renal portal vein is a large vein formed of two branches. The one branch arises in the abdominal wall, while the other passes along the base of the leg and joins the abdominal vein. On each side three dorso-lumbar veins join the renal portal vein. [Illustration: FIG. 6.--Venous System of Xenopus and Rana.] [_In the Frog the abdominal vein is also formed by the union of the two pelvic veins. The pelvic veins, however, lie more superficially than in the Platana. The femoral vein which passes along the front of the thigh divides into two branches, the one branch forming the pelvic vein, the other, joined by the sciatic vein from the muscles and skin of the back of the thigh, forming the renal portal vein extending along the outer side of the kidney. The dorso-lumbar vein from the dorsal wall of the body joins the renal portal vein._] Make a drawing showing the above parts. B. Arterial System. Distend the œsophagus with a piece of cotton wool or paper to show the blood vessels more clearly. Trace out the anterior part of the arterial system, made up of two branches of the truncus arteriosus each of which divides into:-- (_a_) The carotid arch passing to the head region. (_b_) The systemic arch curving round the œsophagus. (_c_) The pulmo-cutaneous arch to the lungs and the skin. _Fourth day._ =Arterial System= (_continued_). 1. Trace the carotid arch, which gives off: (_a_) Two lingual arteries having a common point of origin near the carotid gland. (_b_) A carotid artery passing to the head. At its origin it is slightly swollen into the carotid gland. 2. Trace the systemic arches which run backwards on each side of the body, meeting posteriorly to form the dorsal aorta. Each systemic arch gives rise to an artery which branches into:-- (i) A scapular artery to the pectoral girdle. (ii) A cutaneous artery to the skin. (iii) A brachial artery to the arm. Trace the dorsal aorta backwards, and note that it gives rise to the cœliaco-mesenteric artery about midway between its origin and the origin of the first pair of renal arteries. The dorsal aorta then passes between the kidneys giving four renal arteries to each, and proceeds backwards and divides into an internal iliac artery to each leg. This artery lies between the femoral and the sciatic veins. From each of these arteries a branch is given off which divides into: (i) An iliac artery to the muscles around the ilium. (ii) A cutaneous artery to the skin of the body, just anterior to the leg. (iii) A small artery to the anterior dorsal surface of the hind limb. 3. Trace the pulmo-cutaneous arch, which gives off:-- (_a_) A pulmonary artery, running along the outer side of the whole length of the lung.