CIRCULATION. 



451 



ganglion is fused with the first one or two thoracic ganglia to form the gan- 

 glion stellatum, situated opposite the first intercostal space. At the inferior 

 cervical " ganglion the vagus and the sympathetic part company, the vagus 

 passing caudalward behind the root of the lung and the sympathetic passing 

 to the stellate ganglion, dividing on its way into two portions (the annulus of 

 Vieussens), which embrace the subclavian artery. In many cases the lower loop 

 of the annulus of Vieussens joins the trunk of the vagus caudal to the ganglion. 1 



The cardiac nerves spring from the vagus and the sympathetic nerve in 

 the region of the inferior cervical ganglion. They may be divided into an 

 inner and an outer group. 



The inner group is composed of one medium, one thick, and from two to 

 three slender nerves. The nerve of medium thickness springs from the gan- 

 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 of the cat, drawn from nature after the removal of 



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 



ft .-i ., , *"G Adi; tunning a, tscpitiaut; uuurse tu lilt; uraii; 



the annulus, or from the VagUS 1-1J 5, middle (often called "inferior") cervical gan- 



Centimeters lower down. Each of these glion; 5/ ' communicating branch between middle 



, cervical ganglion and vagus nerve ; 6, stellate gan- 



thlCK branches may be replaced by a glion ; 6', 6" &", spinal roots of stellate ganglion ; 



bundle of finer branches, and in fact 7 ' comm s un a i r n be j ween stellate ganglion and 



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



the description of the cardiac nerves 



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



individual variations. 2 



1 Schmiedeberg, 1871, p. 34. 



2 Details concerning the composition of the cardiac plexuses in the dog are given by Lira 

 Boon Keng, 1893, p. 467. 



FIG. 114. Cardiac plexus and stellate ganglion 



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

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



.R, right ; L, 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; 



