340 THE NERVE SYSTEM 



the acini of the glands, upon the outer surface of 

 the acini; they form plexuses which pierce the acini , 

 wall, and give off minute branches to the gland 

 cells. 



The Afferent or Centripetal Nerves. These end 

 as the former, but as this variety of nerve is sensor, 

 and conveys sensations to the brain and spinal cord, 

 the end-tufts are in intimate relation with specialized 

 end-organs, which are essential to the appreciation 

 of the complex sensations, viz., of sight, the retina 

 in the eye; taste, the taste-buds in the tongue; smell, 

 the olfactory cells in the nasal mucous membrane; 

 hearing, the organ of Corti in the ear. 



In the skin and mucous membranes the axones 

 are in intimate contact with various end-organs which 

 give rise to the numerous conscious sensations of 

 touch, heat, thirst, hunger, and muscle sense, etc. 

 The following are the chief names of the various 

 end-organs : 



1. Free endings in the skin. 



2. Tactile cells of Merkel. 



3. Tactile corpuscles in the papilla of the true skin. 



4. Tactile corpuscles of Meissner. 



5. Pacinian corpuscles found attached to the nerves 

 of the hands, feet, intercostal nerves, and nerves in * 

 other situations. 



6. End-buds of Krause in the conjunctiva, clitoris 

 (female), penis (male), etc. 



The Nerve Plexus. It consists of a number of 

 nerves communicating with other nerves, by means 

 of collateral branches. Some plexuses are formed by 

 direct branches being given off from the spinal cord, as 

 the brachial, lumbar, sacral plexuses; others are formed 

 by the terminal filaments of nerve fibers, as the 

 plexuses in the skin, etc., still others may contain 

 sympathetic nerve fibers derived from the sympathetic 

 system, in addition to the sensor and motor nerves. 



