For, as the subjoined figure (p. 185) shows, the vena cava inferior (_b_), the right auricle (_R.a._), and the vena cava superior and innominate vein (_V.I._) distended with blood seem to form one continuous column, to which the heart is attached as a sort of appendage. This column is, as Aristotle says, vein above (_a_) and vein below (_b_), the upper and the lower divisions being connected διὰ τοῦ κοίλου τοῦ μέσου—or by means of the intervening cavity or chamber (_R.a._)—which is that which we call the right auricle. [Illustration: A dog having been killed by chloroform, enough of the right wall of the thorax was removed, without any notable bleeding, to expose the thoracic viscera. A carefully measured outline sketch of the parts _in situ_ was then made, and on dissection, twenty-four hours afterwards, the necessary anatomical details were added. The woodcut is a faithfully reduced copy of the drawing thus constructed; and it represents the relations of the heart and great vessels as Aristotle saw them in a suffocated animal. All but the inner lobe of the right lung has been removed; as well as the right half of the pericardium and the right walls of the right auricle and ventricle. It must be remembered that the thin transparent pericardial membrane appears nothing like so distinct in nature. _a.b._, Aristotle’s “great vein”; _V.I._, right vena innominata and vena cava superior; _b_, the inferior vena cava; _R.a._, the “hollow middle” part of the great vein or the right auricle; _R.v′_, the prolongation of the cavity of the right ventricle _R.v_ towards the pulmonary artery; _tr_, one of the tricuspid valves; _Pc_, the pericardium; _I.sv_, superior intercostal vein; _Az_, vena azygos; _P.A._, right pulmonary artery; _Br_, right bronchus; _L_, inner lobe of the right lung; _Œ_, œsophagus; _Ao_, descending aorta; _H_, liver, in section, with hepatic vein, vena portæ, and gall-bladder, _gb_, separated by the diaphragm, also seen in section, from the thoracic cavity.]