202 



Prof. A. F. S. Kent. 



situations where the muscular tissue forms a constituent portion of the 

 bundle. 



With regard to the character of the muscle fibres which are found in the 

 bundle, these appear to be of two kinds. Where the muscle is well 

 represented some fibres will usually be found to resemble the tissue present 

 in the neighbouring chamber of the heart. Others, however, are of a 

 different type, and appear as large pale fibres, with but few sarcostyles, those 

 that are present being grouped around the periphery of the fibre. 



If the series of sections be followed further it will be found that the 

 bundle, which at first may be at some distance from the muscle of the heart 

 chamber, gradually approaches this latter, whilst at the same time some of 

 the large pale fibres alluded to as being present in the bundle will be 

 observed to be making their appearance also in the auricular or ventricular 

 tissue, and, after a time, a definite exchange of muscle fibres on a large scale 

 will be observed to take place between the auricle, or ventricle, and the 

 bundle. Fibres which are apparently normal auricular or ventricular tissue 

 approach the connective tissue, pass through as a definite mass of tissue, 

 penetrate the connective tissue sheath of the bundle, and come to lie in its 

 interior. In many cases the amount of muscle entering the bundle in this 

 way is considerable, and much of the tissue is indistinguishable from 

 ordinary cardiac tissue. Some, however, is of the character already 

 described, consisting of fibres with clear centres and sarcostyles scattered 

 around the periphery, and, though smaller, presenting some of the characters 

 of Purkinje fibres. 



It follows from this description that the amount of muscle present in the 

 bundle varies considerably from place to place, and, moreover, that the 

 character of the muscular tissue varies also, being sometimes similar to 

 auricular or ventricular tissue, and having similar staining properties, and 

 sometimes pale fibres containing much faintly staining sarcoplasm with 

 comparatively few darkly staining sarcostyles. 



The nerve fibres which form so important a part of the structures 

 described are of various sizes, from 3 [i to 12 They run, as a rule, a 

 longitudinal or somewhat winding course in the bundle, and may be demon- 

 strated to be connected at various points with the nervous structures lying- 

 in the fat at the auriculo-ventricular junction. They may also be traced 

 leaving the bundle at various points, and passing away through the connective 

 tissue towards the neighbouring tissues. 



From the description which has been given it is apparent that the 

 structure which has been described presents itself as an elongated body of 

 different diameters at different parts of its course, and therefore of a conical 



