the bases of the legs. The pelvic veins occur deep down in the body under the posterior part of the pelvic girdle, which should be cut through in order to see them. At the union of the pelvic veins to form the abdominal vein a small rectal vein, passing along the ventral surface of the rectum, joins the abdominal vein.

In order to make out the femoral and the sciatic veins, turn the Platana over and remove the skin from the back of the leg. The femoral vein may then be seen lying on the surface of the leg, between two of the muscles. By carefully separating these muscles the whole of the femoral vein may be exposed. Deeper down in the muscles of the leg lies the sciatic vein, and, between the sciatic and the femoral veins, the internal iliac artery may be seen running alongside of the sciatic nerve.

Trace the femoral and the sciatic veins forward, and note that they join together at the point where they meet the pelvic veins and then run forward to the kidney as the renal portal vein on each side.

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.

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.

(b) A cutaneous artery, which at first runs forwards to the base of the arm, and becomes spread out on the skin of the back of the head.

[In the Frog

1. The carotid arch gives off:—

(a) A lingual artery supplying the tongue.

(b) A carotid artery, running round the side of the œsophagus, and supplying the head. At its origin it is slightly swollen into the carotid gland.

2. The systemic arches run backwards on each side of the body, and meet posteriorly to form the dorsal aorta. Each systemic arch gives off:—

(a) A subclavian artery to the shoulder and fore-limb.

(b) An occipito-vertebral artery to the head and the vertebral column.

(c) An œsophageal artery to the dorsal wall of the œsophagus.

(d) A laryngeal artery to the larynx.

At the point where the dorsal aorta is formed, note the origin of the cœliaco-mesenteric artery which sends branches to the stomach, liver, intestine, and spleen.

Trace the dorsal aorta backwards and note that it passes between the kidneys, to each of which it gives off four renal arteries and then it divides posteriorly into an iliac artery to each leg. The iliac artery is continued backwards as the femoral artery in the leg.

3. The pulmo-cutaneous arch gives off:—

(a) A pulmonary artery, running along the outer side of the whole length of the lung.

(b) A cutaneous artery, which at first runs forwards and upwards, and then turns backwards, supplying the skin of the back and the sides of the head.]

Make a complete sketch of the arterial system.

Fig. 7.—Arterial System of Xenopus and Rana.

Cut out the heart, leaving attached to it as much as possible of the large vessels.

Note the sinus venosus, truncus arteriosus, auricles, and ventricle.

Open the auricles and observe the division between them and the openings of the veins passing into them.

Make a section through the auricles and ventricle noting the thick muscular walls of the ventricle and the valves between it and the auricles.

Respiratory System and Alimentary System (continued).

1. Remove the mylo-hyoid muscles to expose the hyoid apparatus. Pass a seeker through the glottis to one of the lungs and slit it open with a pair of scissors. Examine the structure of the lung.

2. Remove the whole of the alimentary canal with the lungs, liver, pancreas, and spleen, by cutting through the œsophagus and the large intestine before it joins the cloaca, and detaching it from the roof of the body cavity without