On the nervous system of the heart

Abstract

The author premises a historical notice of the various opinions entertained by distinguished anatomists respecting the nerves of the heart; some having maintained that the human heart is copiously supplied with nerves, and others that it has few or none. In September 1846, the author resolved to dissect, under the microscope, the nerves of the heart while covered with alcohol, as he had done those of the uterus. His examinations of the fœtal heart, of the heart of a child at the age of six years, of the heart of an adult in the sound state, of the human heart greatly hypertrophied, and of the heart of the ox, warrant, he thinks, the following conclusions:—1st, that the blood-vessels and the muscular structure of the auricles and ventricles of the heart are furnished with numerous ganglia and plexuses of nerves which have hitherto been neither described nor represented by any anatomist; 2ndly, that these nervous structures of the heart, which are distributed over its surface and throughout its walls to the lining membrane and columnæ carneæ , enlarge with the natural growth of the heart before birth, and during childhood and youth, until the heart has attained its full size in the adult; 3rdly, that when the walls of the auricles and ventricles are affected with hypertrophy, the ganglia and nerves of the heart are enlarged like those of the gravid uterus; and 4thly, that the ganglia and nerves which supply the left auricle and ventricle in the natural state, are more than double the size of the ganglia and nerves distributed to the right side of the heart. The author observes that the ventricles and auricles of the human heart and of those of the hearts of the larger quadrupeds, are covered with two distinct membranes; the exterior is the serous membrane, connected by cellular tissue with another distinct tunic, which has scarcely, if at all, been noticed by anatomists. This second membrane is stated to have a dense fibrous structure, to be semitransparent, and to resemble in a remarkable manner the aponeurotic expansions, or fascice, covering muscles in other parts of the body; and, like them, it sends numerous fibres or processes between the muscular fasciculi, blood-vessels, nerves, and adipose substance of the heart. This membrane, the author thinks, may appropriately be termed the cardiac fascia , and he states that, through this, after the removal of the serous membrane, there are numerous ganglia and plexuses of nerves visible to the naked eye. If these nerves be traced backwards towards the base of the ventricles, they are seen to terminate in a great ganglionic plexus, situated between the pulmonary artery and aorta; into which plexus branches of nerves enter from the par vagum of each side, the recurrent and the sympathetic nerves. From this great ganglionic plexus, which the author considers to be the root of all the principal cardiac nerves, branches invested with a soft neurilema proceed to the auricles and ventricles, and their septa. Large flat branches of nerves pass from this ganglionic mass to the coronary arteries, the trunks of which they completely surround like a sheath, and all the ramifications of which they accompany, not only over the surface of the heart, but into the muscular substance, and they are distributed with these arteries throughout its walls to the lining membrane. The author also states that there are besides numerous branches of nerves from the great ganglionic plexuses at the base of the heart and surrounding the coronary arteries, with ganglia distributed over the surfaces of both the ventricles, which do not accompany the blood-vessels, but run obliquely across them, and also across the fibres of the muscular coat. These superficial cardiac nerves are described as being remarkably soft, flat, of a grey colour, and somewhat transparent, as had been formerly stated by Scarpa. Towards the left side and apex of the left ventricle, these nerves lie in grooves or depressions of the muscular coat, and spread out into ganglionic enlargements, from which innumerable filaments are sent off laterally to the muscular coat. There are ganglia of considerable size on these superficial nerves where they are crossing the arteries, which send branches to the coats of the vessels, and some of which branches pass down with the vessels into the substance of the heart.