Vascular System (continued).

A. Venous System.

1. Note:—

(a) The heart lying in the thin pericardium, the two auricles, the single ventricle, the truncus arteriosus which divides into two branches.

Remove the pericardium from the heart, and tilt the apex of the heart forwards, noting the sinus venosus into which the right and the left superior venÆ cavÆ (or precavals) and the single inferior vena cava (or postcaval) open.

(b) The veins passing from each side of the sinus venosus. Each superior vena cava is joined by the following branches:—

(i) The external jugular vein from the region of the tongue and the mandible.

(ii) The internal jugular vein from the head and a thick subscapular vein from the shoulder. These veins join the superior vena cava independently of each other so that there is no innominate vein as in the Frog.

(iii) The subclavian vein, made up of a brachial vein from the arm, a cutaneous vein from the skin, and a muscular vein from the abdominal muscles. The cutaneous and the muscular veins are separate veins so that there is no single musculo-cutaneous vein.

[In the Frog the superior vena cava is joined by the following branches:—

(i) The external jugular vein, formed by the union of a lingual vein from the tongue and a mandibular vein from the margin of the lower jaw.

(ii) The internal jugular vein from the head and the subscapular vein from the back of the arm and shoulder, both joining the superior vena cava by a common vein, the innominate.

(iii) The subclavian vein, formed by the brachial vein from the fore-limb and a musculo-cutaneous vein from the muscles of the body and from the skin.]

(c) The hypoglossal and the glossopharyngeal nerves, both running alongside of the lingual artery.

Make an enlarged drawing showing the above parts (a) and (b).

2. Note the inferior vena cava, receiving the renal veins from the kidneys, the hepatic veins from the liver, and opening into the sinus venosus.

3. Trace back the abdominal vein, and note that it is formed by the union of the two pelvic veins, which pass along 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.

Make a drawing showing the above parts.

B. Arterial System.

Distend the oesophagus 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 oesophagus.

(c) The pulmo-cutaneous arch to the lungs and the skin.