THE SI NO- VENTRICULAR BUNDLE. 147 



the fibrous nature of the intervening tissue by no means excluding the possibility of mus- 

 cular fibers running through it and preserving the muscular connection. And in the 

 mammalian heart such a connection appears to exist." 



Kent (1913) finds more than one connection in some hearts he examined and all 

 careful researches will confirm this observation. In the pig I have seen bundles of 

 muscle-tissue streaming down along the outer posterior wall connecting the muscular 

 tissue in the region of the coronary sinus with the ventricular musculature. 



Since then innumerable papers on the subject have appeared and some authors 

 have claimed priority in the discovery of the "bundle," either for themselves or for 

 others. Thus priority was claimed by Paladino (1914) and some authors contend 

 that Kiirschner described the bundle in Wagner's Handbuch. These authors did 

 describe muscular connections, but unlike His, they did not limit these to a restricted 

 area of the septum. Until the monograph of Tawara appeared all work done was 

 in the main confirmatory of His. According to those authors, the muscular con- 

 nection consisted of ordinary cardiac musculature and contained but a negligible 

 amount of nerve-fibers. Tawara was the first to show the connection between the 

 bundle and the Purkinje fibers, although (as I have stated above) Kent had appre- 

 ciated that there was a difference in the histological structure of the bundle and 

 the rest of the cardiac musculature.* 



Tawara called this connection between atria and ventricles and the widely 

 ramifying Purkinje fibers the "Reizleitungssystem." He described nerve-fibers 

 accompanying the system but paid little attention to them. Indeed, his mono- 

 graph was used extensively by the adherents of the myogenic theory as further 

 evidence in their favor. In spite of the careful work of Erlanger and others, it has 

 never been determined definitely whether it is the nerve-fibers accompanying 

 the bundle or the bundle itself that is the conducting element. The term "con- 

 ductive system" is, therefore, only applicable to the nerve-muscle complex. It 

 must be divided anatomically and physiologically into its component parts the 

 nervous mechanism and the muscular mechanism. This is essentially the problem 

 of to-day. Its solution will definitely settle the myogenic or neurogenic theory of 

 the mammalian heart-beat. 



Authors using the term "bundle of His" usually mean the muscular connec- 

 tion. They use the term "Tawara's node" also in the sense that it is a muscular 

 node as described by Tawara. In view of the fact that the bundle is in all 

 instances accompanied by nerve-fibers, we must be more accurate in our ter- 

 minology. Therefore, it has been the author's custom to use the term "conductive 

 system" not in Tawara's sense, but as a designation for the neuro-muscular complex 

 extending from an indefinite area in the wall of the right atrium to the ventricles 

 including the Purkinje fibers. His's bundle or "atrio-ventricular bundle" I have 

 termed the muscular connection between atria and ventricles, not including the Pur- 

 kinje fibers. The term "sino-ventricular bundle" is used to define the muscular con- 



*AlthouRh Tawara's work has been confirmed in this respect by all who have published on the subject since then, we 

 find in the 1912 edition of Quain's Anatomy, Schaefer's Text-book of Mimisrnpic Anatomy, the following statement-', p. 

 200: "In man and most, animals, distinct Purkinje fibers do not exist, but the cardiac fibers are rather larger near the ven- 

 tricular endocardium than elsewhere." And further on: "In animals which have fibers of Purkinje, the ventricular end of 

 the bundle resembles these in structure." Statements like these in text-books which we have learned to look upon as more 

 or less authoritative should be corrected. 



