Till. NI.RVOUS SYSTI M 



179 



be. 1 lie ncurilemma also is continuous throughout the length 

 of the fibre. The medullary sheath, on the other hand, is 

 broken here and there along the length of the fibre at intervals 

 of about .^th of an inch. These breakings are called nodes. 

 Between each two nodes an oval nucleus can generally be 

 found lying just underneath the ncurilemma. 



In some nerve fibres there is no medullary sheath, the 

 neurilemma alone covering the axis cylinder. These are called 

 non-medullated nerve fibres. They are grey in appearance, 

 while the ordinary medullated nerve fibres are white. 



Nerve Cells. On some nerves, usually not far from 

 their origin from 

 the central nervous 

 system, or near their 

 ending in the various 

 organs, there is situ- 

 ated a small knot-like 

 swelling. Such an 

 enlargement iscalled 

 a ganglion. When 

 examined micro- 

 scopically the gan- 

 glion shows, inter- 

 mingled with the 



nerve fibres, or lying ^"- 8 - A large nrrvecell from the anterior horn of the 



round them, a mnn- spinal cortL 



, f 11 11 . I " Nucleus ; ', small body, called the nuclcolus, inside 



IIS ' C the nuclrus ; /, branched processes ; ./, unbranched 



nerve Cells Or gan- proco*s continued into the neuraxis of a motor nerve 



glion cells. The fibre, 

 ganglion cells vary 



much in size in different ganglia, but they arc often about ^J o th 

 of an inch in diameter. The cell substance contains a large 

 round nucleus. Some nerve cells are round, others pear-shaped 

 Hi spindle-shaped, and some are very irregular in outline. They 

 all give off one or more processes, and one of these is a str.md 

 which becomes continuous with the axis cylinder of a nerve 

 fibre. The axis cylinders of all nerve fibres are connected in 

 some place or another with at least one nerve cell. 



These then are the elements of nervous tissue as seen in 

 nerves and ganglia : medullated nerve fibres, non-medullated 



