1 7 4 THE CONTRA CTION OF CA RDIA C MUSCLE. 



a coronary system is present. A well-defined coronary system exists for the 

 ventricle of the tortoise, and the coronary veins empty into the sinus venosus. 

 In the land-tortoise (Testudo grceca) it very frequently happens that one of 

 these coronary veins runs free from ventricle to sinus, so that, as is shown in 

 Fig. 103, a seeker can be slipped under it without injury to any part of the 

 heart ; it also usually happens that one of the nerve trunks which pass from the 

 sinus to the auriculo-ventricular junction, accompanies this free coronary vein, 

 so that in this animal we have a free intracardiac nerve between sinus and 

 ventricle, whose functions can be examined without injury to the rest of the 

 heart. This nerve, which experiment shows to be connected with the vagus, 

 I have called the coronary nerve. In Fig. 104 the appearance of the heart 

 when suspended is shown, and the position of the coronary nerve, C. In 

 the tortoise, as in all other animals, the cardiac ganglion cells are found in 

 connection with the main trunks of the intracardiac vagus nerves. As described 

 in my paper (p. 62), the largest accumulations of them are found at the bifurcation 

 of the larger vagus nerve trunks in the sinus, in the junction-wall or sinus- 



TH 



Fig. 104. — Heart of tortoise as suspended. B, body of tortoise ; 

 TH, thread to lever ; CL, clamp holding aorta. 



extension between the two auricles, and in the termination of this wall in the 

 auriculo-ventricular ring. In all these places the ganglion cells are also 

 found on the smaller branches of the nerves which ramify over the sinus, and 

 form a rich plexus in the junction-wall between the two auricles, and at the 

 junction between auricles and ventricle. The nerves, with their accompanying 

 ganglion cells, are distributed around the whole junction of the sinus and the 

 auricles, and from this ring, as well as from both sides of the junction- 

 wall between the two auricles, nerve fibres with ganglia are plainly seen 

 passing into the auricular tissue ; as the nerves pass further into the tissue 

 the ganglia become more and more scarce, and soon disappear. If, then, we 

 call the junction-wall between the two auricles the flattened part, and the 

 rest of the auricles the bulged part of the auricles, we find that the larger 

 nerve trunks and ganglia of the auricles are found only in those parts of the 

 bulged portion which are in the immediate vicinity of this flattened part. 

 Again, at the junction of the auricles and ventricle the nerve trunks passing 

 from the junction-wall of the two auricles form a rich plexus, containing large 



