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The Nerves of the Atrio -ventricular Bundle. 



By J. Gordon Wilson, M.A., M.B. (Edin.), Hull Laboratory of Anatomy, 



University of Chicago. 



(Communicated by Dr. F. W. Mott, F.E.S. Eeceived January 21, — Bead 



February 11, 1909.) 



[Plates 4—6.] 



Fhysiologists, in explaining the transmission of the wave of contraction in 

 the heart from atrium to ventricle, have alternately leaned towards either 

 the myogenic or the neurogenic hypothesis. Many of the discussions on this 

 subject have been useless and many of the deductions false, because of the 

 misconception of the anatomical facts. For long it was held that though in 

 cold-blooded vertebrates the experiments of Gaskell had settled the question 

 in favour of the myogenic theory, yet in mammals there existed an interrup- 

 tion between the atrial muscle and the ventricular muscle at the atrio- 

 ventricular groove, and that this was opposed to a general acceptance of the 

 myogenic theory. Later anatomical investigation, however, has definitely 

 shown that there exists in all mammals, between the atria and the ventricles, 

 a pathway of modified muscle fibres along which the contraction wave 

 appears to go. This is the atrio- ventricular (auriculo-ventricular) bundle, or 

 bundle of His. The discovery of this muscular connection gave very decided 

 support to the myogenic hypothesis, and at present it would appear that 

 prevailing opinion favours this theory. It receives additional support in so 

 far that in this bundle only a few nerve fibres have as yet been recognised 

 by one or two observers ; some assert that nerves are not present, or, if so, 

 are too few in number to be of any moment. More definite statements have 

 been made by Tawara and Betzer. Tawara (1) found that " in the heart of 

 the calf the atrio-ventricular bundle is accompanied by a very considerable 

 nerve bundle, which runs with the muscle bundle, and in the left ventricular 

 septum nerve, cells are present 1*2 cm. below the aortic valve." In the 

 atrio-ventricular bundle of the sheep only a few nerve bundles were seen, 

 but in the dog, cat, and in man he could find none, though he expressly states 

 that these cannot be excluded, since fine nerve fibres accompany the bundle. 

 Betzer (2) has pointed out that the first ganglion cells that appear in the 

 embryonic heart lie in the atrial septum, immediately above the beginning of 

 the conductive system ; further, that the Burkinje fibres are surrounded by 

 a plexus of non-medullated nerves. 



Such is the present position of our knowledge of the nerve constituents of 



