436 



THE ORGANS 



(p. 425) are extremely varied and complicated. These peripheral 

 terminations are always free, in the sense that, while possibly some- 

 times penetrating cells, they probably never become directly con- 

 tinuous with their protoplasm. 



In the skin, and in those mucous membranes which are covered 

 with squamous epithelium, the nerve fibres lose their medullary 

 sheaths in the subepithelial tissue, and, penetrating the epithelial 

 layer, the axis-cylinder splits up into minute fibrils (terminal ar- 

 borization) which pass in between the cells and terminate there, 

 often in little knob-like swellings (Fig. 302). Such terminal 



Fig. 302. — Free Endings of Afferent Nerve Fibres in Epithelium of Rabbit's Bladder. 

 (Retzius.) 0, Surface epithelium of bladder; b g, subepithelial connective tissue; n, nerve 

 fibre entering epithelium where it breaks up into numerous terminals among the epithe- 

 lial cells. 



fibrils do not penetrate among the squamous cells. Similar ^^ dif- 

 fuse^' endings are found in serous membranes and in simple 

 epitheha, also in connective tissue. In the case of glandular epithelia 

 such endings may, in part at least, be terminations of efferent 

 (secretory) fibres from sympathetic ganglion cells (p. 445). Diffuse 

 endings have also boen described on endothelial surfaces such as 

 endocardium and in smooth muscle. The latter are to be distin- 

 guished from the regular motor endings described below. An impor- 

 tant form of diffuse ending is that found encircUng and ending in 

 the outer root sheaths of hair follicles (Fig. 303). Nerve endings 

 are abundant in the pulp of teeth. There has been some dispute 



