Messenger, Vibrissa; of Mammals. 401 



the hair and enter in few distinct bundles. They run up along 

 the outer sheath proper of the hair beneath the pulvinus and end 

 in the an'nular band above mentioned, or rather bifurcate to form 

 that ring. A few nerve fibers are given off to the pulvinus where 

 scattered ganglion cells are demonstrated in Golgi preparations. 



The perifollicular space is abundantly supplied with blood 

 vessels and is supported by trabeculae of connective tissue. 



The pulvinus is apparently the chief organ of accommoda- 

 tion. It shrinks during the process of preparation for examin- 

 ation but, no doubt, is much larger when fully distended. The 

 variation in size when prepared in various ways indicates its 

 susceptibility. 



The annular nerve band is so situated that when the pul- 

 vinus is not turgid tactile impulses are little felt but when it is 

 turgid the slightest impact produces a marked effect on the 

 nerves surrounding the hair. 



The most striking feature about the whole structure is the 

 arrangement for blood supply. The animal must be able to 

 control this and thus render his vibrissae sensitive when he 

 wishes and practicably insensible when he has no use for them. 

 Probably also there is an efficient reflex control. 



The number and size of the blood vessels and trabeculae 

 indicate that the whole space can be engorged with blood almost 

 instantly, affording very efficient erectile tissue in place of the 

 muscles attached to the ordinary hair. 



DESCRIPTION OF PLATES.^ 



PLATE XXVII. 



Fig. I. Longitudinal section of vibrissa of rabbit The plane of section 

 lies at one side of the hair and its sheath but shows the corium sheath, stroma, 

 pulvinus, peripulvinar space, gland and nerve bundles. 



Fig 2. Similar section cutting the hair and sheath at base but passing 

 lateral to it at higher levels. 



Fig. J. Similar section showing the relations of pulvinus and peri-pulvinar 

 space. (All the above are htcmatoxylin preparations.) 



The figures were all drawn by C. L. Herrick, 



