112 THE ANATOMY OF THE HORSE. 



Dorsal Roots of the Brachial Plexus. These are two b'ranches of 

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

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

 to the inferior cervical ganglion they turn round the inner surface of 

 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 the 

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

 the middle cervical ganglion. 



The Middle 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 branch 

 •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 longus 

 •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 posterior 

 -extremity it is continued into the dorsal cord of the sympathetic. It 

 gives off a cardiac filament. 



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

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

 common arrangement. 



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

 of these (which may be double at its Origin), the smaller of the two, is 

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

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

 [a) The lower' branch, joined by a filament from the vagus, passes 

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

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

 branch continuing backwards on the posterior aorta to dip down 

 between the right and left 'divisions of the pulmonary artery and 

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

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

 & cardiac branch of the right side, is distributed to the roots of the 

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

 right coronary artery, (b) The upper division of the second nerve, 

 passing to the inner side of the left axillary, and along the low T er face 

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

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

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

 that vessel. 



