350 



ELEMENTARY PHYSIOLOGY 



into a number of branches which end in a manner not as 

 yet exactly determined. 



End bulbs are found in tlie papillae of the skin of the 

 lips and in other situations. They are spheroidal and 

 smaller (40/i in diameter) than the tactile corpuscles. 

 They are not all exactly alike, but the commonest form 

 consists of a thin outer sheath or 9apsule which is 

 nucleated and encloses a mass of polygonal cells. The 



nerve-fibre enters the cap- 

 sule and ends among the 

 cells in its interior. 



The great majority, how- 

 ever, of the nerve-fibres 

 going to the skin do not end 

 in any such definite organs. 

 They divide in the dermis in- 

 to exceeding delicate minute 

 filaments, the course and 

 ultimate terminations of 

 which are traced with the 

 greatest difficulty. Some of 

 the finest filaments, however, 

 pass into the epidermis and 

 are there lost among or pos- 

 sibly connected with some 

 of the epidermic cells, especially those of the lower 

 layers. 



Another kind of highly specialised nerve-ending is 

 found on the branches of the nerves which supply the skin 

 of the hand and foot, as they pass through the sub- 

 cutaneous tissue. These are known as Pacinian cor- 

 puscles, called after Pacini, who first carefully described 

 them. From their position they are not, strictly .speaking, 

 sensory endings of nerves in the skin : but they possess 



1 Tlie cf)iijunctiva is the mucous membrane which lines the eyelids and 

 front of the eyeball. 



Fio. 110.— End-bulb from the 

 Human Conjunctiva! (Lono- 

 worth). 



a, the nerve-fibre ; h, capsule 

 with nuclei ; c.c, portions of 

 nerve-fibre inside the end-bulb ; 

 d.e, cells of the core. 



