126 



SENSE OF TOUCH. 



the layers external to it, forms the common integument. In certain 

 parts of the body, and in animals more particularly, the cutis vera is 

 adherent to muscular fibres, inserted more or less obliquely. These 

 form the muscular web, mantle or panniculus carnosus. The layer is 

 well seen in the hedge-hog and porcupine, in which it rolls up the body, 

 and erects the spines; and in birds, raises the feathers. In man, it can 

 hardly be said to exist. Some muscles, however, execute a similar func- 

 tion. By the occipito-frontalis, many persons can move the hairy scalp ; 

 and by the dartos the skin of the scrotum can be corrugated. These 

 two parts, therefore, act as panniculi carnosi. 



In the skin are situate numerous sebaceous follicles or crypts, which 

 separate an oily fluid from the blood, and pour it over the surface to 

 lubricate and defend it from the action of moisture. They are most 

 abundant, where there are folds of the skin, or hairs, or where the sur- 

 face is exposed to friction. We can generally see them on the pavilion 

 of the ear, and their situation is often indicated by small dark spots on 

 the surface, which, when pressed between the fingers, may be forced 

 out along with the sebaceous secretion, in the form of small worms. 

 By the vulgar, indeed, these are considered to be worms. The follicular 

 secretions will engage attention hereafter. 



Fig. 43. 



Sections of Hair. 



a. Transverse section of a hair of the 

 head, showing the exterior cortex, the me- 

 dulla or pith with its scattered pigment, 

 and a central space filled with pigment. 

 b. A similar section of a hair, at a point 

 where no aggregation of pigment in the 

 axis exists, c. Longitudinal section, with- 

 out a central cavity, showing the imbrica- 

 tion of the cortex, and the arrangement of 

 the pigment in the fibrous part. d. Sur- 

 face, showing the sinuous transverse lines 

 formed by the edges of the cortical scales. 

 d . A portion of the margin, showing their 

 imbrication. Magnified loO diameters. 

 (Todd and Bowman.) 



The consideration of the hair belongs 

 naturally to that of the skin. The roots 

 are in the form of bulbs; taking their 

 origin in small follicles or open sacs, 

 hair follicles, formed by the inversion of 

 the cutis, and lined by a reflexion of the 

 epidermis. Around each bulb there are 

 two capsules, the innermost of which is 

 vascular and a continuation of the corium. 

 The hair itself consists of a horny, ex- 

 ternal covering, and a central part, called 

 medulla or pith. When we take hold of 

 a hair by the base, with the thumb and 

 forefinger, and draw it through them from 

 the root towards the point, it feels smooth 

 to the touch; but if we draw it through 

 from the point to the root, we feel the 

 surface rough; arid it offers considerable 

 resistance. It is, therefore, concluded, 

 that the hair is bristled, imbricated or 

 consists of eminences pointing towards 

 its outer extremity, and it is upon this 

 structure, that the operation of felting is 

 dependent the hairs being mechanically 

 entangled and retained in that state by 

 the inequalities of their surface. Certain 

 observers have, however, failed in detect- 

 ing this striated appearance by the aid 



