112 PRACTICAL HISTOLOGY [XIV 



b. Trace as far as possible the course of one of the 

 nerve bundles ; the medulla soon disappears, the fibres, 

 still showing nuclei at intervals, join with the fibres 

 from other bundles to form a coarse plexus ; from this 

 proceeds a plexus of smaller bands which have few 

 nuclei ; finally from this plexus run very fine varicose 

 non-nucleated nerve fibrils in straight lines across the 

 cornea (these fine fibrils may also be seen forming part 

 of the finer bands of the plexus). The coarse plexus is 

 the primary plexus of the cornea. 



12. Neurokeratin netioork. Tease out in clove oil a piece of 

 nerve which has been extracted with alcohol and ether (cp. Notes). 

 Mount in balsam. Note the distinct network in the region formerly 

 occupied by the outer part of the myelin sheath. The size of 

 the meshes varies in different fibres. 



DEMONSTRATIONS. 



1. Transverse sections of sciatic, vagus, and cervical 

 sympathetic nerves. (Cat or rabbit; osmic acid.) Note 

 the relative size of the nerve fibres in the three nerves, 

 and the number of non-medullated fibres in the vagus. 



2. Transverse section of non-medullated nerve 

 (splenic nerve of large animal ; osmic vapour). Note 

 the oval or circular outlines of the fibres ; they vary 

 very little in size, being generally 2/^ in diameter. 



3. Teased degenerating nerve fibres (5 days after 

 section; osmic acid). Note the myelin broken up 

 into masses and globules of various size ; in places a 

 considerable stretch of the nerve may show very little 

 alteration. 



