MAMMALIA. 171 



junction. In the dog, communications between each inferior cervical ganglion and 

 phrenic nerve can be traced. In different animals, the cardiac nerves arise higher 

 or lower according to the position of the heart, and although altogether bearing a 

 considerable resemblance to those in man, neither form such distinct plexuses for the 

 auricles and ventricles, nor a cardiac ganglion, nor distribute so many branches on the 

 large bloodvessels. The size and mode of distribution of the cardiac nerves may be 

 well observed in the heart of the ox very soon after it has been killed, and before the 

 pericardium has become dry : for then every nerve as it passes down on either surface 

 of the heart is accompanied by a vein on each side, by which its breadth is defined. 

 A large absorbent vessel adheres to the front of the nerve, and it is supplied by small 

 arteries in its course from the subjacent vessels. The nerves appear as white lines 

 passing obliquely over each surface, and those of the left ventricle much larger than 

 those of the right. The vein on each side of every nerve is like a thick hair or 

 bristle, and frequently communicates with those accompanying the neighbouring 

 nerves ; the large absorbent vessel on the surface of each nerve becomes very plain 

 after the maceration of the heart in water. The arteries of the nerves are discovered 

 with much greater difficulty, and only after a very minute injection by the coronary 

 arteries. By crossing the muscular fibres and the arteries, the artery of every nerve 

 in its course becomes replenished with blood from branches of different subjacent 

 arteries, and at the same time by this oblique course each descending portion of the 

 muscle derives its nervous filaments from different nerves. By this adopted plan of 

 making the nerves cross the arteries and muscular fibres, every nerve is secure of 

 having its due quantity of blood, notwithstanding the imperfect functions of any 

 particular artery it crosses; any considerable portion of muscle, therefore, cannot have 

 its activity checked. In the porpoise, part of the prolongation passes over, and the 

 rest underneath, the subclavian artery to the first thoracic ganglion, which is large ; 

 it sends a branch on each side to join the recurrent nerve, and branches upwards to 

 the cervical nerves and downwards to the vascular rete on the ribs. The cardiac 

 nerves on the right side begin by a branch from the second cervical ganglion ; it 

 communicates twice with the trunk of the par vagum, and then passes behind the 



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