472 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



inter-ventricular septum and passes, sparsely covered with muscle-bundles, 

 obliquely downward and backward on the right side of the septum. The 

 descendens in its farther course gives off numerous branches to the left ventricle 

 and the anterior part of the septum. Only a few small branches go to the 

 right ventricle. Thus the descendens supplies the septum and the inferior 

 anterior part of the left ventricle. The right coronary artery, imbedded in 

 fat, runs in the right auriculo-ventricular groove around the right side of the 

 heart, supplying the right auricle and ventricle. It is a much smaller artery 

 than either the circumflex or descendens. Each coronary artery keeps to its 

 own boundaries and does not, in the dog, pass into the field of another artery, 

 as sometimes happens in man. 1 



Terminal Nature of Coronary Arteries. The coronary arteries in the 

 dog, as in man, are terminal arteries, that is, the anastomoses which their branches 

 have with neighboring vessels do not permit the making of a collateral circula- 

 tion. Their terminal nature in the human heart is shown by the formation of 

 infarcts in the areas supplied by arteries which have been plugged by embo- 

 lism or thrombosis. That part of the heart-wall supplied by the stopped artery 

 speedily decays. The bloodless area is of a dull white color, often faintly 

 tinged with yellow ; rarely it is red, being stained by haemoglobin from the 

 veins of neighboring capillaries. The cross section is coarsely granular. The 

 nuclei of the muscle-cells have lost their power of staining. The muscle-cells 

 are dead and connective tissue soon replaces them. 2 This loss of function and 

 rapid decay of cardiac tissue would not take place did anastomoses permit the 

 establishment of collateral circulation between the artery going to the part and 

 neighboring arteries. The terminal nature of the coronary arteries in the dog 

 has been placed beyond doubt by direct experiment. It is possible to tie them 

 and keep the animal alive until a distinct infarct has formed. 3 



The objection that one of the coronary arteries can be injected from 

 another, 4 and that therefore they are not terminal, is based on the incorrect 

 premise that terminal arteries cannot be thus injected, and has no weight against 

 the positive evidence of the complete failure of nutrition following closure. 

 The passage of a fine injection-mass from one vascular area to another proves 

 nothing concerning the possibility of the one area receiving its blood-supply 

 from the other. Such supply is impossible if the resistance in the communi- 

 cating vessels is greater than the blood-pressure in the smallest branches of the 

 artery through which the supply must come. It is the fact of this high resist- 

 ance, due to the small size of the communicating branches, which makes the 

 artery " terminal." This condition of high resistance is really present during 

 life, or infarction could not take place. 



The terminal nature of the coronary arteries is of great importance with 

 regard to the part taken by them in the nutrition of the heart. Being ter- 



1 Cohnheim and v. Schulthess-Rechberg, 1881, p. 511. 



2 See also the description by Kolster, 1893, p. 14, of the infarctions produced experiment- 

 ally in the dog's heart. 



3 Kolster, 1893, p. 14 ; Porter, 1893, p. 366. * Michaelis, 1894, p. 289. 



