Mammalia: Nervous System 



669 



pressures, tensions, or bending strains incurred by the shaft of the 

 hair are transmitted to its root and there stimulate the follicular 

 nerve-endings. (For a demonstration, touch very gently the tip of a 

 single hair on the ear of a sleeping cat.) The vibrissae, long stiff hairs 

 projecting laterally from each side of the upper lip ("whiskers" of dog 

 and cat), are an important sensory apparatus. It is to be emphasized 

 that the hair itself serves only for mechanical, not nervous, transmis- 

 sion. The nervous receptors are at the root. 



Aside from the nerve-endings at the roots of hairs, mammalian 

 skin is abundantly supplied with receptors which are stimulated by 

 one or another of the various external agencies which give rise to 

 sensations of touch (more accurately, pressure), heat (temperatures 

 above that of the body), cold (temperatures below that of the body), 

 and pain. Free nerve-termination is found in the skin of all parts of 

 the body, especially in the epidermis. There are also highly specialized 

 receptors in which the nerve-endings are in close relation to a cell or a 

 group of cells, or to a connective-tissue investment of some sort (p. 



Stratum 

 corneum 



Fig. 502. Section perpendicular to the surface of the skin of the palmar side 

 of a finger, showing two papillae, one of which (at right) contains a tactile cor- 

 puscle. (Schafer.) (Magnified about 200 diameters.) (Courtesy, Schafer: "Quain's 

 Anatomy," London, Longmans, Green & Co., Ltd.) 



