Of TMI: Q 



epithelial phi:: i> diH'erent. h, ,- papilla arises at 



tin- surface of t lit- >km ami i> foiv.-d do\\ n by a p 

 growth; in tin- former t In- epit hdial plug first sink > i.- nder- 



lyin.ir t i in- and 1 1 1 the li;iir papilla in formed by a 



corium. 



The ^notion arises, \vhichoft! 



IK con-idered the uioro primitive? In my opii 



'} of the .is is 



unquestionably the ampler and leas complete con* i \\\ which 



the latter i- derivable and tlirou^li \\iiidi it Ls explainable. Tlie 

 hairs >ink into the undtM-lying tissue for the purpose of \ 



i-hiiKMit and at t acliincnt. A parallel is furnished by the 

 deyelopmenl >i' tln> tt-rtli. In th selachians the latter arise (so 



far as they arc dcvdojitd a vc >t nu't nn-s in the ll 



papillfd which grow from the oorinm into tin- cj>idci-in: -'osts 



and Amphibia, on tlic contrary, tlm tcctli, wliicli an- found 

 trilmttd over 'vxiciivivc ai-cas in the oral mucous membrane, are 

 established deep down in that membrane, for epithelial pi 

 tlic ioi-ni of plu:< lir>t >ink down into tin**-- tissue, ai. 



i- only Mil>s<><iu(>ntly that the dental papillre are formed by . 

 of growth in the connective ti the bottom of the 



downgrowth. 



Let us return aft hirther developoieni 



the hair: thi> take> place in thf same manner in tx>th the cases 

 distin^iuMn-d above. The i-pith.-lial celU which cover the papilla; 

 multiply and are dilVerent iated into two parts (fig. 292 C) ; ! 

 into cells that are more remote from the papilla', that become 

 spinllo-.-hap d and united into a small cone, and that by cornific;i 

 ice the tir-t point <>f the hair (Aa), and secondly into cells \\ 

 immediately invest the papilla, remain protoplasmic, and c 

 the matrix the hair-bulb i//:) by means of which the further 

 irrowth of the hair takes place. The c< 



rapidly im tea>e b\ division, are added below to the first-formed part 

 of the hair, and by coi niticat ion cont i-ibulo to its elonga 



The hair in ]>rocess of development on the papilla at first lies 



wholly concealed in the skin and is enveloped les by cells of 



the epithelial plug, at the bottom of which the first trace of it was 



fornu d. l-Yoni this investment are formed the outer and the inner 



/ f/, f > root and D aw and iw). Of these the 



i (<i>r) OMIMMS < f >mall protoplasmic cells and is cc: 



externally with the m 



