MEDULLATED NERVE-FIBRES 



459 



Many of the nerve-fibres of which the anterior roots 

 are composed may be tiaced into the anterior cornu, and, 

 indeed, into the nerve-cells lying in the cornu, while 

 those of the posterior roots, for the most part, pass into 

 this posterior column of white matter (Fig. 143, 6). 



4. The Minute Structure of MeduUated Nerves.— 

 The white matter of the spinal cord consists chiefly of 

 nerve-fibres ; we may therefore, with advantage, consider 



Fio. 145.— Transverse Section of a Medium-sized Medullated Nerve. 



ep, ep, general connective tissue sheath or epineurium ; /, /, /, bundles 

 of nerve-fibres bound together by the perineurium per, per, per ; A,A,V, 

 blood-vessels ; L, lymphatic vessel. 



the structure of these nerve-fibres before dealing in detail 

 with the minute structure of the cord itself. 



If a small piece of a nerve, which may be easily obtained 

 from the leg of a freshly killed frog or rabbit, be teased 

 out with needles on a glass slide and examined under a 

 microscope it is seen to be made up chiefly of minute 

 fibres. When the nerve has been suitably hardened it 

 becomes possible to cut a transverse section of it ; if this 

 section be similarly examined the cut ends of the fibres 



