THE SHEATH OF THE BUNDLE OF HIS 69 



cardial connective tissue. It is remarkable that the sheath can 

 be so easily dissected loose from the bundle which it covers and 

 that it can nevertheless withstand the pressure necessary to inject 

 it so extensively. Although a rapid diminution of pressure 

 undoubtedly occurs as the fasciculi branch and anastomose, 

 the pressure at the point of injection is relatively great; never- 

 theless the sheath withstands it, if ordinary care be used. Fur- 

 thermore, in view of the reduction of pressure which must result 

 from the progressive division and anastomosis of the fasciculi the 

 extent to which the sheath can be injected is very great. 



The question might well be asked whether or not this system, 

 which can be injected so easily, is in relation with the lymphatic 

 system. A consideration of the origin and the termination of the 

 sheath will furnish the answer. It has been shown that the tissue 

 forming the sheath is continuous, on the one hand, with the peri- 

 mysium of the auricular muscle, on the other with the perimy- 

 sium of the ventricular fibers. Consequently, if we look upon the 

 sheath as composing the walls of a lymph space we must neces- 

 sarily look upon the perimysium in a similar way, and accept the 

 fact that this lymph space extends out around the fasciculus of 

 heart muscle cells and around the single cells. Such a concep- 

 tion would of course seem untenable. 



The functions of the sheath lie outside the scope of this paper, 

 excepting so far as the idea of a lubricating mechanism is con- 

 cerned. If, by a bursa, we understand a structure distinct from 

 the sheath, the existence of such a bursal space was not confirmed 

 by this investigation. On the other hand, if the inflated connec- 

 tive tissue sheath was mistaken for a bursa, the interpretation of 

 its function as a lubricating apparatus seems impossible. Other 

 writers, notably Tawara, Keith, Fahr, and Monckeberg, have 

 spoken of its function as one of isolation and insulation. How- 

 ever, Dogiel, whose opinion is worthy of great consideration, has 

 recently stated that the existence of such a sheath has never been 

 satisfactorily proven, and hence feels under no necessity to ascribe 

 to it a function. The writer offers the facts herein reported as 

 further proof of the indisputable existence of the sheath as a very 

 definite structure which isolates the atrio-ventricular system from 

 the rest of the heart, even to its terminations. 



