112 THE ANATOMY OP THE HORSE. .- 



Dorsal Roots of the Brachial Plexus. These are two branches o: 

 the 1st and 2nd dorsal nerves respectively. They will be found at th« 

 upper part of the 1st and 2nd intercostal spaces. After giving branches 

 to the inferior cervical ganglion they turn round the inner surface o) 

 the 1st rib, close to its upper extremity. 



The Sympathetic Nerve. The cervical cord of the sympathetic, 

 which in the neck is fused with the vagus, separates from it at thi; 

 entrance to the chest, and terminates in a stellate greyish ganglion— 

 the middle cervical ganglion. 



The Iliddle Cervical Ganglion. — This will be found within the 1st rib, 

 or in front of it, at the line of contact of the trachea and oesophagus, 

 A thick connecting branch continues it up to another enlargement — the 

 inferior cervical ganglion. The middle cervical ganglion has a brand 

 of communication with the vagus, and gives off two or three cardiac 

 nerves. 



The Inferior Cervical Ganglion is placed a little above the preceding, 

 to which it is connected by a short thick nerve. It rests on the longuf 

 colli, between the vertebral and superior cervical arteries. It is joined 

 by the vertebral nerve, and by short branches from the inferior primary 

 divisions of the 8th cervical and first two dorsal nerves. By its posterio: 

 extremity it is continued into the dorsal cord of the sympathetic. Il 

 gives off a cardiac filament. 



Cardiac Nerves of the left side. — These nerves, like many others 

 have a variable disposition, but the following is probably the mosi 

 common arrangement. 



The middle cervical ganglion detaches two cardiac nerves : (1) On( 

 of these (which may be double at its origin), the smaller of the two, ii 

 distributed to the great arteries in the anterior mediastinum. (2) Th( 

 other immediately divides into two branches — a lower and an upper 

 {a) The lower branch, joined by a filament from the vagus, passei 

 beneath the arch of the left axillary in company with the vagus, and 

 reaching the angle of bifurcation of the common aorta, it divides, om 

 branch continuing backwards on the posterior aorta to dip dowi 

 between the right and left divisions of the pulmonary artery am 

 gain the left auricle, while the other descends along the commoi 

 aorta, and, uniting at the origin of the right coronary artery witl 

 a cardiac branch of the right side, is distributed to the roots of th^ 

 great arteries and to the ventricles, the largest branches following th^ 

 right coronary artery. (6) The upper division of the second nerve 

 passing to the inner side of the left axillary, and along the lower fac 

 of the trachea, unites with a right cardiac filament, crosses to th 

 right of the common aorta, and is reflected round that trunk to gaii 

 the left coronary artery, its divisions following the main branches c 

 that vessel. 



