THE DISCOVERERS OF THE THORACIC CARDIAC NERVES

By G. A. G. MITCHELL, Manchester University

BECAUSE of their importance in connection with the surgical treatment of angina pectoris the thoracic cardiac nerves are small objects of great interest. It is therefore surprising that amongst the many articles and books dealing with the subject of cardiac innervation which have appeared since these nerves were first described, not one provides accurate information about their discovery. Judging from some of these writings, their very existence is not universally recognised, so it may be advisable to explain briefly that the cardiac plexus, amongst many other branches, receives slender contributions from the second, third, fourth and possibly fifth thoracic and that these constitute the thoracic cardiac nerves. Apart from the works mentioned later, no details of the thoracic cardiac nerves have been found in any of the great anatomical mono- graphs, atlases and textbooks published during the nineteenth century. Early this century Mollard (1908) produced an elaborate monograph on the cardiac nerves, but he described none arising from the sympathetic trunks below the level of the first , although he quoted from the works of such men as E. H. Weber (1815) and G. Valentin (1843) who had found cardiac branches arising at a lower level. Those writing exhaustive monographs seldom succeed in assimilating com- pletely all the information contained in the works listed in their impressive bibliographies, and Mollard was no exception. J. Dogiel, either alone or in collaboration with others, published many papers on the heart over a period of about thirty years, but he too remained unaware of the existence of the thoracic cardiac nerves. Perman (1924) and Miiller (1924) both wrote at length about cardiac innervation and the former described thoracic cardiac nerves in the calf. Dresbach and Waddell (1926) detected connections between the cardiac plexus and the thoracic sympathetic trunks as far down as the fifth ganglia ; Kondratjew (1926) found these nerves in man ; and Cannon, Lewis and Britton (1926) realised from their experiments in cats that complete elimination of cardiac accelerator fibres required extirpation of the sympathetic ganglia as low as the sixth or seventh thoracic segments. Woollard (1926) published another long article about cardiac inner- vation in the same year, but admitted that he had relied on writers such as Mollard, Perman and Miiller for his survey of the earlier literature. In 1927 and 1928 two excellent articles appeared containing descriptions, amongst other things, of the thoracic cardiac nerves in man. They were written by Braeucker (1927) and by Ionescu and 156 NERVES 157 DISCOVERERS OF THE THORACIC CARDIAC

has assumed Enachescu (1928), and every authority since apparently ctua y that they first discovered these nerves in human subjects ( in Ionescu and Enachescu first published their findings brie y 19 7> first iscovere and in this article they made the definite claim that they and Smithwic the thoracic cardiac nerves in man.) Thus White (194) attributes it to onescu give the honour to Braeucker, and Kuntz (1946) to onescu and Enachescu. Nonidez (1939) also accorded the honour " Anu new an and his co-workers," and he added : In the same year cardiac nerves o t Schuralew published their contributions on the etic rar? cat and dog, respectively, in which the thoracic cardiosympat " 1 ) are described and represented ; incidentally Wolhyns (192 the same eitsc ri . described and illustrated these nerves in the calf in of Ionescu an Braeucker's article is more detailed than that the discoverer o e Enachescu and he himself made no claim to be Cc ' thoracic cardiac nerves, he did infer, with every justi although ore. so accurate y e that no one had ever described or illustrated them branches He mentioned that F. Meckel had described cardiac J. (1817) is at another in from the upper thoracic ganglia ; and point arising rom article he stated that Valentin (1843) revealed branches running an t a the second and third thoracic ganglia to the cardiac plexus, branc es rom Swan (1830) and Bourgery (1844) also realised that of the the upper thoracic ganglia shared in the innervation thatca^' e Careful examination of Meckel's (1817) work, however, shows thoracic ia did not describe cardiac nerves arising from the upper gang t e said . From but from the uppermost thoracic ganglion. He whic uppermost thoracic ganglion branches go off medially pass to the partly to the lower part of the Longus cervicis (colli), partly however, cardiac plexus, partly to the which^is, One chiefly constituted by the vagi, and partly to the aorta. The fact that must be in connection with this statement. P?^n^ emphasised ' a stellate the inferior cervical cardiac nerve might be derived from cervica an or rootlets derived from separate inferior ganglion, by a at a date, y first thoracic ganglia, was recognised still earlier pro by Vieussens (1716). . The honour of discovering the thoracic cardiac nerves belongs who first neither to Meckel nor Valentin, but to E. H. Weber (1815) first described t em detected them in a calf, and to J. Swan (1830) who did not mention the thoracic in man. Curiously enough Weber (1815) the interest lent cardiac nerves in his text, and indeed, apart from small thesis on to his work by the illustration of these nerves, this be The ner e comparative anatomy would not otherwise noteworthy. third and fourth thoracic in question are shown arising from the second, t e e t si ganglia in a rather crude diagram (Plate IV) depicting to the leave of the of a calf. The explanatory legends plate to the no doubt that Weber realised the nerves he illustrated passed t one heart, and intercommunicated with one another en route. are thicker than the point he stated that the nerves in the calf's heart 158 G. A. G. MITCHELL corresponding filaments in man, but he did not indicate anywhere that thoracic cardiac nerves exist in man similar to those in the calf. Joseph Swan's atlas, published in 1830, was based on dissections which gained two collegial anatomical prizes of the Royal College of Surgeons in 1825 and 1828, and in most respects its plates of the nerves, and particularly those of the , surpass in detail and accuracy those decorating modern textbooks. He depicted and described right and left thoracic plexuses, formed by branches from the inferior cervical and upper four thoracic ganglia, which contributed to both cardiac and pulmonary plexuses. This is the earliest reference one has traced to cardiac contributions in man arising below the level of the first thoracic ganglion. The thoracic plexus of Swan should not be confused with the ramus splanchnicus supremus of Wrisberg (1800), reputedly formed at the root of the neck by contributions from the cervical cardiac, recurrent laryngeal and main vagal nerves. He said that this ramus, after a variable downwards course within the thorax, occasionally joined the posterior vagal trunk or entered the abdomen alongside the aorta to end in the coeliac plexus ; along its course it might receive filaments from the thoracic sympathetic trunk and distribute offshoots to the aorta, thoracic duct, pericardium, lungs and oesophagus. The existence of Wrisberg's complicated highest splanchnic nerve is by no means certain, but it is certain that some of the filaments he described do exist, although they are not arranged quite in the way he imagined. It is probable he observed the filaments now described as the thoracic cardiac nerves in part of their course, but failed to trace them into the cardiac plexus. It is imprudent in investigations of this type to state with absolute certainty who first described any particular anatomical fact, because no worker has access to, or the time to read, everything written on the subject. With this reservation, one believes that Ernest H. Weber and Joseph Swan deserve the credit for discovering the thoracic cardiac nerves in the calf and man respectively, at least one hundred years earlier than is usually stated.

My thanks are due to Professor W. Schlapp and Mr F. C. Hirst for providing certain exact translations from German articles.

REFERENCES

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