NOTES ON THE PILOMOTOR SYSTEM

Abstract

1. In the baboon (Papio anubis) the exhibition of aggressive resentment is accompanied by a bristling of the hairy cape which covers the neck, shoulders, and upper part of the back.This area includes the scalp as far forward as the eyebrows, and the whisker‐like growths on the cheeks; the neck, especially at the sides and back; and the lateral and dorsal aspects of the thorax. At the sides, the area covers the shoulders and spreads down the upper arm on the outside. Caudally it passes back as far as the last pair of ribs.Stimulation of the upper cut end of the cervical sympathetic nerve, under full anæsthesia, produces an erection of hair in the corresponding half of the upper part of this area. This includes the scalp, eyebrow, cheek, neck, and shoulder. The lower limit of this area is bounded by the proximal part of Sherrington's “dorsal and ventral axial lines” of the forelimb.This area does not correspond with the whole of that which bristles under emotional excitement. The posterior part, which is not affected on stimulation of the cervical sympathetic, may be caused to bristle on stimulation of the anterior spinal roots in the thoracic region at least as low as the tenth pair.2. In the sooty monkey (Cercocebus æthiops) stimulation of the upper cut end of the cervical sympathetic nerve causes an erection of the hair on the forehead, eyebrow, and cheek of the corresponding side. No pilomotor effect was detected upon the scalp, neck, or shoulder.3. In the rhesus macaque (Macacus rhesus) erection of the hair of the back and tail is sometimes exhibited by fully grown individuals when in a state of anger.In these individuals stimulation of the upper cut end of the cervical sympathetic nerve, under full anæsthesia, produces erection of hair over the whole of the corresponding half of the scalp, including the forehead and eyebrow, and also over the whole of the cheek. This area is more extensive than was previously noted in Macacus rhesus.Stimulation of the caudal segment of the cut lumbar sympathetic nerve causes an erection of hair over the whole of the corresponding haunch, buttock, and ischial region round the callosity. There is also erection of the tail‐hairs along its whole length, but this effect spreads slightly across the mid‐line of the tail. The oral boundary of this area in the macaque monkey appears to correspond with the proximal part of the “dorsal axial line” of Sherrington.4. In the cat, electrical stimulation of the cut surface of the cord at the level of the first cervical segment produces a bilateral pilomotor effect in the tail when the stimulus is applied within the area marked in the diagram. This pilomotor effect is accompanied by a lashing movement of the tip of the tail from side to side, and by a great rise in the arterial blood‐pressure. The same effects accompany stimulation applied at the level of the pyramidal decussation in the medulla oblongata. The point yielding the effect is indicated in a figure. A similar effect is also obtained on stimulating the cross section of the mid‐brain at the level of the anterior colliculus. This is also indicated in a diagram. In addition to the described effects, there is sometimes an unsheathing of the claws.