A text-book of physiology for medical students and physicians . as repre-sented in Fig. 226, to form a system of strands that can be traced * See Retzer, Archiv f. Anatomie, 1904, p. 1, and Anatomical Record,2, 149, 1908; Braeunig, Archiv f. Physiologie, 1904, suppl. volume, p. 1;Tawara, Das Reizleitungssystem des Saugethierherzens, Jena, 1906. t DeWitt, Anatomical Record, 3, 475, 1909. THE HEART BEAT. 531 over the inner surface of the ventricles, constituting what wereformerly designated as Purkinje fibers. The auriculoventricularnode in the interauricular septum is connected with the muscula
A text-book of physiology for medical students and physicians . as repre-sented in Fig. 226, to form a system of strands that can be traced * See Retzer, Archiv f. Anatomie, 1904, p. 1, and Anatomical Record,2, 149, 1908; Braeunig, Archiv f. Physiologie, 1904, suppl. volume, p. 1;Tawara, Das Reizleitungssystem des Saugethierherzens, Jena, 1906. t DeWitt, Anatomical Record, 3, 475, 1909. THE HEART BEAT. 531 over the inner surface of the ventricles, constituting what wereformerly designated as Purkinje fibers. The auriculoventricularnode in the interauricular septum is connected with the muscula-ture of the auricles, and through muscle bundles in the septum withthe remnant of sinus tissue (sino-auricular node) at the mouth ofthe superior vena cava. The main bundle and the larger branchesof this system are surrounded by fibrous tissue, and it is uncertainwhether or not it actually contracts during the beat of the heart,but there is little doubt that it constitutes a conducting system ofmodified muscular tissue through which the excitation is conveyed. Fig. 226.—The auriculoventricular bundle and its terminal ramifications in the interiorof the ventricles (from model constructed by Miss De Witt on basis of dissections). The divi-sion of the bundle into right and left branches is shown, and the ramifications of each of thesebranches in the interior of the right and left ventricles. The branching system in the left ven-tricle is incomplete in the model, as the outer wall of this ventricle had been removed in thedissection. from right auricle to the ventricles, and perhaps from the sinusregion first to the auricles and then to the ventricles. The A-Vnode and the main bundle in the human heart are small in size—about 18 mm. long, and from to mm. wide, and they and theirdependent system of fibers or strands in the interior of the ventriclesconstitute, according to Keith and Flack,* a remnant of theoriginal invagination of muscular tissue from the auricular ring(F
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