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.