THE TACTILE HAIR OF THE WHITE RAT 



S. B. VINCENT 



Frovi the Oiological Laboratory of the Northwestern University Medical School 



THIRTEEN FIGURES 



CONTENTS 



I. General description : 1 



II. Historical 6 



III. Methods of study 8 



IV. Innervation 8 



V. Comparative anatomy 16 



VI. Function 20 



VII. Summary • 24 



Bibliography 26 



I. GENERAL DESCRIPTION 



The principal tactile hairs of the white rat are found on the 

 upper lip arranged in rows on either side of the nasal fossae. 

 The longer and larger of these hairs are the most lateral ones of 

 the second, third and fourth rows counting from below. Besides 

 these there are a few scattered hairs on the lower lip, on the 

 cheeks, above the eyes and on the fore limbs at the wrist joint. 

 We are chiefly concerned with the vibrissae of the upper lip which 

 in an active animal are in constant motion. 



By the term 'hair' we usually mean the shaft which projects 

 from the surface of the skin, but considered as a sense organ the 

 important part is the follicle beneath the surface which encloses 

 the base of the shaft. We may think of it as an invagination of 

 the epidermis and see in it the usual skin layers somewhat modi- 

 fied under the different conditions of growth. 



The follicle is a long oval in shape varying in length from 1 

 to 5 mm. and in width from 0.5 to 2 mm., and it is surrounded by 

 two sheaths, a dermal and an epidermal. As we look at the folli- 

 cle in a longitudinal section it appears like two pockets, one within 



1 



THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 23, NO. 1 

 FEBRUARY, 1913 



