320 JAMES EDWARD ACKERT 



hair, and usually end in slight enlargements (fig. 9, eh), some of 

 which are merely small varicosities, while others resemble the 

 minute end-knobs seen in the free nerve terminations in the 

 epidermis. In certain cases there are no enlargements, but in 

 these instances the terminal fibers are flattened. This type of 

 nerve ending undoubtedly corresponds to the well known nerve 

 ring and 'palisade' described first by Arnstein ('76), and recog- 

 nized since by Bonnet ('78), Szymonowicz ('01), and Sabussow 

 ('10). Merkel ('80) described a similar end-apparatus on a 

 common hair in the lip of a cat. The "termaisons en fourchette" 

 of the Hoggans ('83) and the nerve rings of Retzius ('94), Van 

 Gehuchten ('96) and Ostroumow ('00) are probably correspond- 

 ing nervous structures. 



3. Nerve fibrils in the outer root sheath. At the level of approxi- 

 mately the lower third of the root of the hair, medullated nerves 

 penetrate the connective tissue layers of the follicle. When the 

 hyaline membrane is reached they divide and run for a short 

 distance on or near its surface. These nerve fibers give off a 

 few strong non-medullated fibrils which pierce the glassy mem- 

 brane, and end in the outer root sheath, usually taking a hori- 

 zontal position in the latter (fig. 9, eo). The nerve endings of 

 this type are found in a slight swelling of the root sheath, which 

 may correspond to the superior swelling described in typical 

 sinus hairs. So far as the writer has been able to ascertain, 

 nerve endings of this type have not previously been described 

 in the pelage hair of the bat. While such examples are not numer- 

 ous, yet they seem to him to be genuine. Nerve endings in the 

 form of tactile corpuscles were described by Szymonowicz ('01) 

 in the outer root sheath of a hair in the face of Vesperugo serotinus. 

 The same observer, in 1909, mentioned the finding of Merkel's 

 corpuscles in this layer of the follicle in man. Retzius ('94) 

 described a nerve fiber in the outer root sheath of a hair of a mouse, 

 and Vincent ('13) found nerve fibrils in this layer of the sinus 

 hair of the rat. 



