152 



Mr. J. G. Wilson. 



[Jan. 21, 



the atrio-ventricular bundle. Although a vast amount of work has been 

 done on the nerves of the heart generally, yet, so far, but little attention has 

 been directed to this particular and definite strand. In this preliminary 

 paper I have limited the report to the muscle band as it passes from the 

 atrium to the ventricle, and shall not discuss the nerve constituents in the 

 connections of the atrio-ventricular bundle with the ordinary muscle of the 

 atrium or of the ventricle ; that is, 1 limited the investigation to that part 

 which extends from a point in the bundle towards the coronary sinus over 

 the bifurcation into right and left branches and down these into the right 

 and left ventricles. These parts are represented in figs. 1 and 2 (Plate 4). 



Historical. — The first specific demonstration of the presence of a muscular 

 connection between the atrium and ventricle was given by Gaskell in 1883. 

 Previous to that time many writers had declared that such a connection 

 existed, but their statements were indefinite. Por instance, Paladino(3) is 

 referred to by Bardeleben as having found that " die Vorhofsmuskulatur 

 endet nicht an den Annuli fibro-cartilaginosi, sondern geht grossentheils in 

 die Ventrikelwand und die Papillarmuskeln weiter." It was Gaskell (4) who 

 first definitely showed that in the tortoise the contraction wave spreads from 

 the sinus over the auricle to the ventricle by means of the muscular connec- 

 tion which exists between the three parts of the heart at the sino-auricular 

 and auriculo-ventricular grooves. He found that at the sino-auricular 

 junction the fibres of the sinus form a circular muscle-ring from which the 

 fibres of the auricle take origin. Prom this origin the fibres of the auricle, 

 after ramifying in all directions, approach and get attached to the upper and 

 middle part of the auriculo-ventricular groove, forming a ring of muscle 

 fibres from which in turn the fibres of the ventricle take origin. By experi- 

 mentally sectioning between the two auricles, and by removal of the visceral 

 pericardium, he was able to show that the " ventricle contracts in due 

 sequence with the auricle, because a wave of contraction passes along the 

 auricular muscle and induces a ventricular contraction when it reaches the 

 auriculo-ventricular groove." The integrity of the whole muscle at the 

 auriculo-ventricular groove is unnecessary for this sequence, for there exists 

 a definite track along which the wave of contraction passes. Histologically 

 he found that the muscle fibres present in the auriculo-ventricular muscle- 

 ring differed from the muscle cells of the auricle and ventricle both in the 

 size of the nucleus and the character of their striation. 



In spite of Gaskell's work, the hypothesis generally accepted was that the 

 contraction wave cannot be myogenic because in mammals there occurred a 

 distinct break between the muscle of the atria and the muscle of the 

 ventricles. It was held that the atrial fibres and the ventricular fibres 



