;6 THE CARDIAC NERVES. 



[Percussion. As the heart is a solid organ, and is surrounded by the lungs, which contain 

 air, it is evident that the sound emitted by striking the chest over the region of the former 

 must be different from that produced over the latter. Not only is there a difference in the 

 sound or note emitted, but the " sensation of resistance " which one feels on percussing the two 

 organs is different. We may ascertain 



1. The superficial or absolute cardiac dulness. 



2. The deep or relative dulness.] 



[Superficial Cardiac Dulness. This theoretically is the part of the heart in direct contact 

 with the chest-wall and uncovered by lung, but obviously as the lungs vary in size during 

 respiration, it must be smaller during inspiration and larger during expiration. It forms a 

 roughly triangular space, whose base cannot be accurately determined, as the heart-dulness 

 merges into that of the liver, situate below it, but it corresponds to a horizontal line 1\ inches 

 long, extending from the apex-beat to the middle of the sternum. The internal side corre- 

 sponding to the left edge of the sternum is 2 inches long, and reaches from the junction of the 

 fourth costal cartilage with the sternum apex of the triangle to the sternal end of the base 

 line. The superior, outer, or oblique line, 3 inches in length, is somewhat curved, and passes 

 downwards and outwards from the apex of the triangle to the apex of the heart.] 



[Deep Cardiac Dulness. By this method theoretically we seek to define the exact limits of 

 the heart as a whole, and thus to ascertain its absolute size, and of course percussion has to be 

 done through a certain thickness of lung tissue, and hence one must strike the pleximeter 

 forcibly. It extends vertically from the third rib and ends at the sixth, but owing to the 

 cardiac merging in the hepatic dulness, this lower limit cannot be accurately ascertained ; while 

 transversely at the fourth rib it extends from just within the nipple line to slightly beyond the 

 right of the sternum. By these means we may detect increase in the size of the heart or altera- 

 tions in the relation of the lungs to the heart, fluid in pericardium, &c. ] 



[Auscultation. This is one of the most valuable methods, for by it we can detect variations 

 and modifications in the healthy sounds of the heart, the rhythm and frequency of the heart- 

 beat, the existence of abnormal sounds, and their exact relation to the normal sounds, also 

 their characters and relation to the cardiac cycle, and the direction in which these sounds are 

 propagated ( 54).] 



57- INNERVATION OF THE HEART. [Intra- and Extra-Cardiac Nervous 



Mechanism. When the heart is removed from the body, or when all the nerves 

 which pass to it are divided, it still beats for some time, so that its movements 

 must depend upon some mechanism situated within itself. The ordinary rhythmical 

 movements of the heart are undoubtedly associated with the presence of nerve 

 ganglia, which exist in the substance of the heart the intra-cardiac ganglia. But 

 the movements of the heart are influenced by nervous impulses which reach it from 

 without, so that there falls to be studied an intra-cardiac and an extra-cardiac 

 nervous mechanism.] 



The cardiac plexus is composed of the following nerves: (1) The cardiac 

 branches of the vagus, the branch of the same name from the external branch of 

 the superior laryngeal, a branch from the inferior laryngeal, and sometimes branches 

 from the pulmonary plexus of the vagus (more numerous on the right side) ; (2) 

 the superior, middle, inferior, and lowest cardiac branches of the three cervical 

 ganglia and the first thoracic ganglia of the sympathetic ; (3) the inconstant twig 

 of the descending branch of the hypoglossal nerve, which, according to Luschka, 

 arises from the upper cervical ganglion. From the plexus there proceed the deejy 

 and the superficial nerves (the latter usually at the division of the pulmonary 

 artery under the arch of the aorta, and containing the ganglion of Wrisberg) 

 ( 370). The following nerves may be separately traced from the plexus : 



(a) The plexus coronarius dexter and sinister, which contains the vaso-motor 

 nerves for the coronary vessels (physiological proof still wanting) as well as the 

 nerves (sensory ?)^ proceeding from them (to the pericardium 1). 



(b) Intra-cardiac nerves and ganglia. The nerves lying in the grooves of the 

 heart and in its substance contain numerous ganglia (Remak), and are regarded as 

 the automatic motor centres of the heart. A nervous ring containing numerous 

 ganglia corresponds to the margin of the septum atriorum there is another in the 

 auriculo-ventricular groove. Where the two meet, they exchange fibres. The 



