

THE INNERVATION OF THE HEART. 445 



of vital processes per se. Indeed, in the heart they do naught 

 else than in other parts of the organism. The general motor 

 system (sympathetic) insures the tonic contraction of the coro- 

 naries and smaller vessels; the vagus, when need be, assumes 

 control, to increase or reduce the rapidity of the organ's con- 

 tractions. "The rich nervous supply of the heart is derived 

 from the coronary plexuses," says Piersol, "and includes numer- 

 ous medullated fibers coming from the pneumo gastric as well as 

 the non-medullated sympathetic fibers proceeding from the 

 cervical ganglia. Numerous microscopical ganglia are found 

 along the course of the large nerve-trunks accompanying the 

 branches of the coronary arteries, especially in the longitudinal 

 interventricular and in the auriculo-ventricular furrows. Many 

 additional small groups of ganglion-cells occur within the mus- 

 cular tissue associated with the fibers supplying the intimate 

 structure." 



The similarity between the innervation of the heart and 

 that of the organs of the digestive tract is recalled in the above 

 quotation by the conjoined sympathetic and vagus plexuses, 

 which form around the coronaries what we have termed the 

 "extrinsic" nerves: i.e., those that regulate the amount of blood 

 admitted into an organ. The analogy further asserts itself when 

 the distribution of the terminal fibers, as depicted by Langer- 

 hans and Eanvier, is reviewed. Berdal refers to this feature 

 -of the terminal supply as follows: "The nerve-fibers which 

 penetrate the depths of the cardiac muscle form, on the surface 

 of the fasciculi, a long-meshed plexus which sends into the 

 interior of these fasciculi still finer fibers. These fibers form 

 a second net-work, the elongated meshes of which present the 

 dimensions of a muscular fiber; but, instead of containing the 

 muscle-fibers in their meshes, the latter seem to traverse them 

 longitudinally." 



We can, therefore, base our deductions, as regards the func- 

 tions of the terminal subdivisions of the sympathetic and vagus 

 nerves in the heart-muscle, upon the analogy which the func- 

 tions of these nerves in other organs suggest. Their similar 

 distribution, extrinsic and intrinsic, in all the organs that they 

 jointly supply, including the heart, seems to us to afford con- 

 siderable likelihood that their role is similar in the latter organ 



