THE CIRCULATION OF THE BLOOD. 291 



allied animals, there is every reason for believing that the results so 

 obtained hold true, with minor exceptions, for the heart of the 

 mammal. 



THE RELATION OF THE NERVE SYSTEM TO THE HEART. 



In all classes of vertebrates the heart not only contains localized 

 collections of nerve-cells, but is also connected with the central nerve 

 system by two or three sets of nerve-fibers. 



/|In the frog heart a group of nerve-cells is found in the sinus at its 

 junction with the auricle, known as the crescent or ganglion of Remak; 

 a second group is found at the base of the ventricle on its anterior 

 aspect, and known as the ganglion of Bidder; a third group is found 

 in the auricular septum, known as the septal ganglion, or v. Bezold's 

 or Ludwig's. The majority of the cells are situated on the surface of 

 the heart just beneath the pericardium. From the cell-body fine 

 non-medullated fibers pass into the substance of the heart, to be 

 histologically and physiologically related with the muscle-fiber. 

 These nerve-cells were formerly regarded as the, sources of the 

 stimuli for the heart's activities y/They are ''regarded by Gaskill 

 as trophic in function, and exerting a favorable influence on the nutri- 

 tion of the heart-muscle./^ 



In the dog heart the nerve-cells are not arranged in such definite 

 groups, but are distributed in the terminations of the venae cavse, 

 pulmonary veins, the walls of the auricles, and in the neighborhood 

 of the base of the ventricles. 



The nerves which connect the heart with the central nerve 

 system are two: viz., the vagus or pneumogastric, and the sympa- 

 thetic. A 



^Phe Vagus. Histologic investigation has shown that the vagus 

 nerve-trunk contains medullated fibers of large and small size.$ Ex- 

 periment has shown that the large fibers are afferent, the small fibers 

 efferent^L. function. | The small efferent fibers are the peripherally 

 coursing axons of nerve-cells situated in the gray matter beneath the 

 floor of the fourth ventricle at the tip of the calamus scriptorius. The 

 exact course of these fibers is not definitely known. According to 

 some investigators, they leave the medulla by way of the spinal 

 accessory nerve and enter the trunk of the vagus through the internal 

 or anastomotic branch; according to recent investigations made by 

 Schaternikoff and Friedenthal, they leave the medulla along the path 

 by which the afferent fibers enter and never become associated with 

 the spinal accessory nerve at its origin. 



^Below the origin of the inferior or recurrent laryngeal nerves, 

 branches containing the efferent fibers are given off, which pass to the 

 heart^The terminal branches of the fibers are not distributed 



