Neuro- Muscular Structures in the Heart, 



203 



or fusiform shape, into the composition of which both nerve fibres and 

 muscle fibres of two distinct varieties enter, surrounded by a distinct con- 

 nective tissue sheath in which large lymphatic spaces exist, and being 

 abundantly supplied with blood. Further, that these structures can be 

 shown to be connected with the muscular tissue of the auricle or of the 

 ventricle on the one hand, and with the nervous structures lying in the 

 auric ulo- ventricular groove on the other. 



It will be at once apparent that the structures described have many 

 points in common with the neuro-muscular spindles found in skeletal 

 muscle. The association of nerve and muscle fibres in a definite structure, 

 the modification of the muscle fibres, the general shape, even the connective 

 tissue sheath with its lymphatic spaces, all recall the structure of neuro- 

 muscular spindles. 



And it may be that, just as the structure of the two organs is similar, so 

 also are their functions. In the neuro-muscular spindles of skeletal muscle 

 we see organs destined for the reception of impulses from the muscle fibres — 

 impulses which pass to a centre consisting of nerve cells and throw it into 

 activity, i.e. the organ is a receptive one and functions as a part of a 

 reflex arc. 



In the neuro-muscular structures described we see organs which from 

 their structure and connections may well function as receptive organs, 

 which may well be roused to activity by the muscle, and transmit impulses, 

 it may be, to the local centre, i.e. to the nerve cells in the auriculo- 

 ventricular groove. 



And, further, if this is so, it is difficult to avoid the suggestion that we 

 see here, as yet imperfectly described and obscure in some of its workings, 

 a local mechanism whose function it is to place in communication the various 

 chambers of the heart, and to correlate their activities — a mechanism con- 

 sisting of receptive organ, afferent path, centre, efferent path, and distributing 

 organ, and constituting a local reflex arc, which may perhaps exhibit only 

 an occasional activity, the co-ordination of the cardiac rhythm being, as a 

 rule, provided for by the muscular connections of the auriculo-ventricular 

 bundle, but which may be capable of controlling that co-ordination when the 

 bundle is no longer perfect. 



This research has been assisted by a grant from the Research Fund of the 

 University Colston Society. 



