Von Cyon and Ludwig in 1866 showed that central stimulation of the sectioned superior cardiac nerve in rabbits caused a fall in the blood pressure and a slowing of the heart action. Two reflex effects resulted from electrical stimulation of this nerve: a vasodilating stimulation of the vasomotor center in the medulla oblongata and the slowing effect on the heart center. These authors named them "depressor" nerves. Köster, Tschermak and Schumacher demonstrated that these nerves terminated on the arch of the aorta and further designated them aortic nerves. The bilateral aortic or depressor nerves have been considered ever since to possess the function of reflex regulation of the circulation.
Hering1 announced in 1924 that in addition to the two known depressors he had found two more nerves having the same action. These were the nerves of the carotid sinus bearing the anatomic name of rami carotici nervi glossopharyngei. These