VS HANDBOOK OF PHYSIOLOGY. 



single and undivided through nearly its whole course, yet as ifc ap- 

 proaches the region in which it terminates, individual fibres break up 

 into several subdivisions before their final ending. 



Nerve Collaterals. It has been discovered through the researches 

 of Golgi, and confirmed by the further studies of Cajal and other an- 

 atomists, that each individual nerve-fibre in the central nervous system 

 gives off in its course branches which pass out from it at right angles 

 for a short distance, and then turn and run in various directions. These 

 branches are called collaterals. They end in fine, brush-like termina- 

 tions, known as end-brushes, or in little bulbous swellings which come 

 in close contact with some nerve cell (fig. 103). 



Fig. 103. Terminal ramifications of a. collateral branch belonging to a fibre of the posterior 

 .Column in lumbar cord of an embryo calf. 



These collaterals form a very important part of the nerve-unit. At 

 the point where they are given off, there is usually a little swelling of 

 the neuraxou proper. 



The nerve-fibre itself continues on and finally ends in various ways, 

 according to its function and the organ with which it is connected. In 

 the nerve-centres, that is, in the brain and spinal-cord, the different 

 nerve-fibres end just as the collaterals do, by splitting up into fine 

 branches which form the end-brushes. Collaterals of the nerve-fibres and 

 end-brushes are chiefly found in the nervous centres. The nerve-fibres 

 of the peripheral nerves end in the muscles, glands, or special sensory 

 organs, such as the eye and ear. Here, however, some analogy to the 

 end-brush can also be discovered. As the peripheral nerve-fibres ap- 

 proach their terminations, they lose their medullary sheath, and consist 

 then merely of an axis-cylinder and primitive sheath. They then lose 

 also the latter, and only the axis-cylinder is left. Finally, the axis- 



