CHAPTER XXXV. 



TOUCH. TEMPERATURE SENSATIONS. PATN. COMMON 



SENSATIONS. SMELL. TASTE. THE MUSCULAR SENSE. 



THE skin is very abundantly supplied with afferent nerve- 

 fibres, and from it we get several very distinct kinds of sen- 

 sations; it is therefore not surprising that nerve-fibres are 

 found to end in it in different ways, but at present we are not 

 able to associate satisfactorily any one particular variety of 

 cutaneous nerve-ending with the origination of the impulses 

 which lead to the occurrence of any one kind of the skin sen- 

 sations. 



Many cutaneous afferent nerve-fibres end in a very simple 

 way: they form plexuses in the outermost layer of the dermis 

 and then, losing the medullary sheath, the axis cylinders enter 

 the epidermis and there break up into extremely minute fila- 

 ments which ramify among the cells of the Malpighian layer 

 and terminate there without any special end organs. Other 

 fibres have special terminal apparatuses, known as (1) tactile 

 cells; (2) end bulbs ; (3) tactile corpuscles ; (4) Pacinian 

 bodies. 



The Tactile Cells lie usually in the deepest layer of the 

 epidermis, but sometimes are found also in the dermis. They 

 ace larger and more granular than the neighboring epidermic 

 cells, more oval, and stain more deeply with some reagents, 

 especially gold chloride. Minute axis-cylinder branches can 

 be traced into close relation to them, and according to some 

 histologists end in flat expansions closely applied to the tactile 

 cells, while others believe the nerve-filament to be directly 

 continuous with the cell substance. These cells are especially 

 abundant in the epidermis lining the root-sheaths of such 

 tactile hairs as the ' ' whiskers " of a cat, but they exist in 

 many if not most regions of the human skin. 



The End Bulbs lie in the dermis of certain regions as the 

 lips, but they are mainly confined to the conjunctiva and to 

 the mucous membrane lining the mouth and that of the lowest 



576 



