100 



AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



glion itself. The thick branch rises from the trunk of the vagus near the 

 origin of* the inferior laryngeal nerve about 1.25 centimeters caudal to the 



inferior cervical ganglion. It can be 

 easily followed to its final distribution. 

 It passes behind the vena cava superior, 

 perforates the pericardium, and runs 

 parallel with the ascending aorta across 

 the pulmonary artery, on which it lies 

 in the connective tissue already divided 

 into two or three tolerably thick twigs 

 or spread in a fan of smaller branches. 

 These now bend beneath the artery, 

 pass round its base on the inner side, 

 and reach the anterior inter-ventricular 

 groove. Here they spread over the 

 surface of the ventricle. The slender 

 branches leave the vagus trunk caudal 

 to the branch just described. 



The outer group comprises two thick 

 branches — namely, an upper nerve, 

 springing from the ganglion or from 

 the trunk of the vagus near it, and a 

 lower nerve, from the lower loop of 

 the annulus, or from the vagus 1-1 £ 

 centimeters lower down. Each of these 

 thick branches may be replaced by a 

 bundle of finer branches, and in fact 

 the description of the cardiac nerves 

 here given can be regarded as a close approximation only, so frequent are the 

 individual variations. 1 



In the rabbit the cervical sympathetic and the vagus trunk are not joined, as 

 in the dog, but run a separate course. Cardiac fibres from the spinal cord reach 

 the lower cervical and first thoracic ganglion (ganglion stellatum) along their 

 rami eommunicantes and pass to the heart by two sympathetic cardiac nerves, 

 one from the interior cervical ganglion and one from the ganglion stellatum. 

 The arrangement of the cardiac nerves in the cat is shown in Figure 29. 

 In the frog the cardiac nerves, both vagal and sympathetic, reach the heart 

 through the splanchnic branch of the vagus. The sympathetic fibres pass out 

 of the spinal cord with the third spinal nerve, through the ramus comniunicans 

 of this nerve into the third sympathetic ganglion, 2 up the sympathetic chain 

 to the ganglion of the vagus, and down the vagus trunk to the heart. 



1 Details concerning the composition of the cardiac plexuses in the dog are given by Lim 

 Boon Keng: Journal of Physiology, 1893, xiv. p. 467. 



' It is probable that the fibres of spinal origin end in the sympathetic ganglia, making con- 

 tacta there with sympathetic ganglion cells, the axis-cylinder processes of which pass up the 

 cervical chain and descend to the heart in company with the vagus. 



-;-' l 



Fig. 29.— Cardiac plexus and stellate ganglion 

 of the cat, drawn from nature after the removal of 

 the arteries and veins ; about one and one-half times 

 natural size (Boehm, 1875, p. 258): 



R, right; /..left: 1,1, vagus nerve; 2, cervical 

 sympathetic ; 2', annulus of Vieussens ; 2", thoracic 

 sympathetic; 3, recurrent laryngeal nerve; 4, de- 

 pressor nerve, entering the vagus on the right, on 

 the left running a separate course to the heart ; 

 5, middle (often called "inferior") cervical gan- 

 glion ; 5', communicating branch between middle 

 cervical ganglion and vagus nerve; 6, stellate gan- 

 glion; (I', 6" 6'", spinal roots of stellate ganglion; 

 7, communication between stellate ganglion and 

 vagus ; 8', 8", 8'", cardiac nerves. 



