On the Nerve Supply of the Heart of Flying-Squirrel

Abstract

The GERLACH's plexus found in the pericardium of flying-squirrel is in best development in the best-developed parts of the pericardium around the origins of the a. pulmonalis and the aorta, containing ganglia, large and small. The development of this plexus is better in the flying-squirrel's than in the hedgehog's heart. Small ganglia are also in sporadic existence in the myocardium too, as in the human (SETO) and the canine (SATO) hearts. In the ventricles where the epicardium is thin, neither GERLACH's plexus nor ganglia are found.The intramyocardiac secondary and tertiary plexuses originating in the epicardiac GERLACH's plexus are far better developed than those of hedgehog. In the well developed endocardium some rather thick nerve bundles originating in these plexuses are often discovered.The GERLACH's plexus is composed of non-medullated sympathetic and vagal parasympathetic fibres in the main, but some thick medullated sensory fibres are present among them. It is of interest that these sensory fibres are more numerous in flying-squirrel than in dog or hedgehog.The ganglia in the heart of flying-squirrel are also better developed than those of hedgehog. The ganglion cells in them, however, are as poorly developed in flying-sqnirrel as in hedgehog and much more poorly than in man and dog, showing the features of infantile type cells comparable to the sympathetic cells in human fetus (UTSUSHI, TAKAHASHI).The terminations of the vegetative nerve fibres are here too in the form of terminal reticula (STOHR). These reticula never send out side branches into the supplied cells but come into control over these cells by mere contact.The area of distribution of sensory fibres in the heart of flying-squirrel as well as in man and other mammals is limited to the auricles and does not extend into the ventricles. The terminations of these sensory fibres are formed only in the myocardium and the endocardium. It is of interest that the terminations in the endocardium are larger both in quantity and individual size in flying-squirrel than in dog and hedgehog.The sensory terminations in the myocardium are incomparably simpler than those in man, but are more complex than the intramyocardiac terminations in the heart of hedgehog, and also than the branched terminations in dog, excepting the terminations Type I concerned with blood-pressure falling reflex. That is, unbranched Type terminations are very small in number, so the terminations are mostly branched ones and these include even rather complex ones in formation.These intramyocardiac sensory terminations may be classified again into the three subtypes according to the courses of the fibres as follows: 1. branched terminations composed of fibres showing not much winding in their courses; 2. those composed of fibres showing perceptible winding and 3. those including fibres running looped or twisted courses. Of these, the latter two subtypes often comprise cnsiderably complex terminations and in many cases resembling those in the human heart (AIBA) - a very interesting finding. Often the fibres in all these terminations show marked change in size and end always sharply.The sensory terminations found in the endocardium consist in unbranched and simple branched ones. The latter may be classified into the same three types as in the above, but here their courses are much simpler in all the subtypes. Change in size during the courses of the fibres is equally frequent and some of them often end in close vicinity of the endothelial cells.