The baroreceptor endings of the sinus nerve extend into the region of the external media, to the media-adventitia border, and into the adventitia of the wall of the carotid sinus. The size of the receptors, tightly filled with mitochondria, varies between 600 and 5,700 nm in diameter. The endings are accompanied by densely structured Schwann’s cells, come into contact with the muscular-elastic system or are surrounded by the collagenous material of the vessel wall. This functional junction makes the reception of the tension in the vessel wall possible. Glycogen granules could be demonstrated in some axon endings. In kittens and older cats, numerous receptors were regularly found with various degrees of structural change: homogeneous and lamellar transformation of mitochondria, lamellar aggregates, lysis of axoplasm matrix, irregularities of tubules and vesicles. These modifications may be evaluated as the morphological expression of degeneration and regeneration processes. Physiological detrition is considered to be the cause for thi