Ventricular Nerve Cells in Mammals

Abstract

IT is widely believed that, in mammals generally, cardiac nerve cells are limited to the atria, extending at the most as far distally as the base of the ventricles near the atrioventricular sulcus. We have examined histologically the hearts of representatives of a number of orders of mammals, namely, Monotremes, Marsupials, Insectivora, Rodentia, Carnivora, Cetacea, Artiodactyla, Perissodactyla, Chiroptera, Menotyphla and Primates. In most of these, no nerve cells were found in the epicardium, endocardium or myocardium of the ventricles. Only in Cetacea and Artiodactyla (see later) are ventricular nerve cells abundant; literally, many thousands extend widely over both ventricles in the epicardium, and numerous nerve cells accompany the atrioventricular bundle and its right and left limbs in the ventricular endocardium, but are not found elsewhere in the endocardium or in the myocardium. In Perissodactyla, no nerve cells were found in the ventricles; the difference between Artiodactyla and Perissodactyla in this respect lends support to the modern tendency (based on other morphological differences) to discontinue the use of the term ‘Ungulates’ to include both these groups, and to raise both to equivalent ordinal rank. Among Artiodactyla, the Ruminants show a much more extensive distribution of ventricular nerve cells than do the Non-ruminants; in this respect the Cetacea resemble the Ruminants, a feature that supports other morphological evidence of affinity between these two groups.