LIGATURE OF THE CORONARY ARTERIES. 75 



heart. Where they pass into veins, several unite at once to form a thick venous 

 trunk whereby an easy passage is offered to the blood. The veins are provided 

 with valves so that (1.) during systole of the right auricle the venous stream is 

 interrupted; (2.) during contraction of the ventricles the blood in the coronary 

 veins is similarly accelerated as in the veins of muscles. 



The coronary arteries are characterised by their very thick connective tissue and 

 elastic intima, which perhaps accounts for the frequent occurrence of atheroma of 

 these vessels (Henle). Some observers (Hyrtl and Henle) maintain that the 

 coronary arteries do not anastomose, but this is denied by Langer and Krause. 

 Many of the small lower vertebrates have no blood-vessels in their heart-muscle, 

 e.g., frog (Hyrtl). 



Coronary Circulation. The phenomena produced by partial oblitera- 

 tion or ligature of the coronary arteries are most important. In man 

 analogous conditions occur, as in atheroma or calcification of these 

 arteries. 



Ligature of the Coronary Arteries. S6e and others ligatured the 

 coronary arteries in a dog, and found that after 2 minutes the cardiac 

 contractions gave place to twitchings of the muscular fibres, and 

 ultimately the heart ceased to beat. Ligature of the anterior 

 coronary artery alone, or of both its branches, is sufficient to produce 

 this result. 



If the coronary arteries be compressed or tied in a rabbit in the 

 angle between the bulbus aortse and the ventricle, the heart's action is 

 soon weakened, owing to the sudden anaemia and to the retention of 

 the decomposition products of the metabolism in the heart-muscle (v. 

 Bezold, Erichsen). Ligature of one artery first affects the corresponding 

 ventricle, then the other ventricle, and, last of all, the auricles. Hence, 

 compression of the left coronary artery (with simultaneous artificial 

 respiration in a curarised animal) causes slowing of the contractions, 

 especially of the left ventricle, whilst the right one at first contracts 

 more quickly and then, gradually, its rhythm is slowed. The contrac- 

 tions of the left ventricle are not only slowed but also weakened, 

 whilst the right pulsates with undiminished force. Hence it follows 

 that as the left half of the heart cannot expel the blood in suffi- 

 cient quantity, the left auricle becomes filled, whilst the right 

 ventricle, not being affected, pumps blood into the lungs. (Edema of 

 the lungs is produced by the high pressure in the pulmonary circula- 

 tion, which is propagated from the right heart through the pulmonary 

 vessels into the left auricle (Samuelson and Griinhagen). 



According to Sig. Mayer, protracted dyspnoea causes the left ventricle 

 to beat more feebly sooner than the right, so that the left side of the 

 heart becomes congested. Perhaps this may explain the occurrence 

 of pulmonary oedema during the death agony. 



Cohnheim and v. Schulthess-Rechberg found after ligature of one of the large 

 branches of a coronary artery in a large dog, that at the end of a minute the 



