Chap. XII. ERECTION OF THE HAIR. 297 



tion of the hair in many insane patients, in part to their 

 minds being always somewhat disturbed, and in part to 

 the effects of habit, — that is, to the hair being frequently 

 and strongly erected during their many recurrent parox- 

 ysms. In patients in whom the bristling of the hair is 

 extreme, the disease is generally permanent and mortal; 

 but in others, in whom the bristling is moderate, as soon 

 as they recover their health of mind the hair recovers 

 its smoothness. 



In a previous chapter we have seen that with animals 

 the hairs are erected by the contraction of minute, un- 

 striped, and involuntary muscles, which run to each 

 separate follicle. In addition to this action, Mr. J. Wood 

 has clearly ascertained by experiment, as he informs 

 me, that with man the hairs on the front of the head 

 which slope forwards, and those on the back which slope 

 backwards, are raised in opposite directions by the con- 

 traction of the occipito-frontalis or scalp muscle. So 

 that this muscle seems to aid in the erection of the hairs 

 on the head of man, in the same manner as the homolo- 

 gous panniculus carnosus aids, or takes the greater part, 

 in the erection of the spines on the backs of some of the 

 lower animals. 



Contraction of the platysma myoides muscle. — This 

 muscle is spread over the sides of the neck, extending 

 downwards to a little beneath the collar-bonjes, and up- 

 wards to the lower part of the cheeks. A portion, called 

 the risorius, is represented in the woodcut (M) fig. 2. 

 The contraction of this muscle draws the corners of the 

 mouth and the lower parts of the cheeks downwards and 

 backwards. It produces at the same time divergent, 

 longitudinal, prominent ridges on the sides of the neck 

 in the young; and, in old thin persons, fine transverse 



wrinkles. This muscle is sometimes said not to be under 

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