THE CIRCULATION. 255 



ventricle to auricle or from auricle to ventricle ; this is not a property 

 of nerve-fibers. Engelmann by zigzag cuts probably cut all nerve-fibers, 

 yet conduction ensued from end to end of the muscle. 



In the myogenic theory, the heart-muscles have the property of 

 automatic rhythm^ and the power and supremacy is greatest at the 

 venous end of the heart. Hence this part of the heart contracts first 

 and the wave spreads to the auricle and then to the ventricle. 



Porter has found that the apex of a dog's heart, which histologists 

 tell us has no nerve-cells, when fed by its nutrient artery with warm 

 defibrinated blood-beats for several hours. 



According to Gaskell and Engelmann, the nerve-ganglia do not 

 play any part in the movements of the frog's heart. According to 

 their idea the sinus sends out impulse-waves through the muscular 

 structure of the heart. When the first Stannius ligature is applied 

 it blocks the waves running from the sinus to the right auricle. 

 Here the sinus continues beating, but the remainder of the heart is 

 quiet. If, now, you tie a ligature in the auriculo-ventricular groove 

 ef this quiescent heart, then the ventricle beats. The ligature or 

 compressor at this point is said to stimulate the ventricle. 



In mammals the sinus venosus of the frog has been included in 

 the right auricle at the point of entrance of the vena? cavse, and is thus 

 directly continuous with the auricular wall. 



It was formerly supposed that there was no muscular connection 

 existing between the auricles and ventricles, but the bundle of His 

 has been found to extend from the auricles to the ventricles. 



This bundle is about 2 indies in length,, about 1 / 10 of an inch in 

 width, and about V 10 of an inch in thickness. Tawara has found a 

 nervous network in this bundle of His. 



Auriculo-ventricular Bundle of His. 1 According to Tawara, this 

 bundle starts in the vicinity of the anterior edge of the coronary vein, 

 running forward on the right side of the auricular septum below the 

 oval foramen, closely hugging the auriculo-ventricular septum. Just 

 above the median flap of the tricuspid valve this bundle forms a node 

 and from this node a process arises which pierces the fibrous septum, 

 runs along dorsal to the ventricular septum and divides into two main 

 branches, passing obliquely downwards, on each side of the septum of 

 the ventricle under the endocardium. The right and left branch of 

 the main bundle, each enclosed in a connective-tissue sheath of its 

 own, isolated from other muscles, pass a long way down the septum 

 and in the lower third of ventricular cavities, with the trabecula. 



1 British Medical Journal, 1906, p. 1107. 



