712 NERVOUS SYSTEM OF THE HORSE 



side it lies upon the longus colli and the trachea, on the left side upon the same 

 muscle and the oesophagus. It is flattened, very irregular and variable in outline, 

 and is blended more or less with the first thoracic ganglion. It is connected by 

 large gray rami with the ventral branches of the last two cervical nerves, and by 

 small filaments with the recurrent nerve. It receives a nerve — termed by Schmaltz 

 the nervus transversarius — which accompanies the vertebral artery; through it 

 rami come from the second to the sixth cervical nerves inclusive. 



A middle cervical ganglion may he present, and occurs oftenest on the right 

 side. It lies on the carotid artery an inch or two in front of the first rib and is 

 intercalated in the vago-sympathetic trunk. 



The cardiac nerves (Nn. cardiaci) are formed by branches from the inferior 

 cervical and first thoracic ganglia, together with twigs from the sympathetic trunks 

 and the vagi. They form a plexus (P. cardiacus) on the ventral face of the trachea 

 with each other and with branches of the vagus and recurrent nerves. They are 

 subject to considerable variation, but their general arrangement may be stated as 

 follows : 



(a) On the right side there are usually two cardiac nerves. Of these one 

 passes back with the vagus in the angle between the right brachial artery and the 

 common carotid trunk, pierces the pericardium, crosses the aortic arch, and divides 

 into branches Avhich are mingled with those of the left nerves. The second crosses 

 obliquely over the right face of the trachea and joins the vagus, where the latter 

 gives off the right recurrent nerve; a small plexus is formed here, from which 

 two or three cardiac branches are detached. These pass back beneath the trachea 

 and ramify on the atria and ventricles. 



(6) On the left side there are commonly three cardiac nerves. One of these is 

 distributed to the great vessels in the anterior mediastinum. The largest passes 

 back at first with the vagus l^eneath the arch of the left l)rachial artery, inclines 

 downward, perforates the pericardium, and divides into two branches. One 

 branch passes beneath the bifurcation of the pulmonary artery and is distributed 

 to the left atrium. The larger branch dips in between the aorta and the pulmonary 

 artery, gives twigs to these vessels, and ramifies on the ventricles, especially along 

 the course of the right coronary artery. The third nerve crosses the deep face of 

 the left brachial artery, passes back below the trachea, and unites with filaments 

 of a right cardiac nerve. It passes around the aorta and ramifies chiefly along the 

 course of the left coronary artery on the left face of the ventricles. 



3. The thoracic part (Pars thoracalis systematis sympathici) extends below 

 the costo-vertebral joints from the inferior cervical ganglion to the upper border 

 of the diaphragm, and passes between the latter and the psoas minor to be con- 

 tinued by the abdominal part. 



The trunk is concealed in the first part of its course by the outer border of the 

 longus colli, but further back it is visible under the pleura. 



The ganglia are arranged segmentally at each intercostal space and partly on 

 the heads of the ribs. They are flattened and are small and fusiform, with the 

 exception of the first. This (G. thoracale primum) is extensive, irregularly quadri- 

 lateral in outline, and is united with the inferior cervical ganglion. The ganglia 

 are connected with the thoracic nerves by white and gray rami communicantes. 



The visceral branches comprise aortic, cardiac, pulmonary, and oesophageal 

 branches, and the splanchnic nerves. The aortic branches ramify on the thoracic 

 artery, forming around that vessel the thoracic aortic plexus (P. aorticus thoracalis). 

 The cardiac branches concur with those of the vagus in forming the cardiac plexus 

 (P. cardiacus). From this branches go to form the coronary plexuses (P. coronarii) 

 along the course of the vessels of like name. The pulmonary branches join with 

 corresponding branches of the vagus and filaments from tlie cardiac plexus in 

 forming the pulmonary plexus (P. pulmonalis) at the root of the lung. Branches 



