Chap. XIX] THE NERVOUS SYSTEM 369 



1. Nerve-fibres which terminate in the brain or spinal cord 

 split up into end arborizations. 



2. Sensory nerve-fibres ending at the periphery of the body 

 terminate in two ways : — 



(a) Inter-epithelial arborizations. 



(b) Organules. 



3. Motor nerve-fibres ending in voluntary muscles terminate in 

 motor plates. 



4. JNIotor nerve-fibres ending in involuntary muscles (such as in 

 the viscera) terminate in a plexus. 



End arborizations. — If the nerve-fibre is to terminate while 

 still lying in the mass of the nervous system, its axis cylinder may 



Fig. 176. — Sensory Nerve Terminations in Stratified Pavement Epi- 

 thelium. (Kirkes.) 



split up at the termination into a number of short filaments called 

 end arborizations, which interlock with the dendrites of another 

 neurone, or the axis cylinder may send out collaterals which inter- 

 lock with dendrites. Thus an individual neurone would serve only 

 as a relay station. 



Inter-epithelial arborizations. — This is the most common mode 

 of termination of sensory nerves. The nerve-fibres pass to the 

 surface either in the skin or mucous membrane ; the neurilemma 

 and medullary sheath disappear, the naked axis cylinder subdivid- 

 ing into minute arborizations that ramify between the epithe- 

 lial cells of the surface of the body. This method is the one in 

 which nerves terminate in various glands, hairs, teeth, tendons, etc. 



Organules. — Some of the highly complex special sensations 

 need very complex end organs for their reception. These end or- 

 gans are modified epithelial cells and are called organules. The 

 axis cylinder subdivides into arborizations as described above; 

 2b 



