TISSUES OF THE BODY. 



305 



probable that a physiological decay with fatty degeneration also takes 

 place to a limited extent. 



Calcification of this tissue is rarely seen. 



Neoplasis of striped muscle, at points where it did not previously 

 exist, is of very unt'requent occurrence. A certain number of those few 

 cases which have been up to the present recorded have reference, strange 

 to say, to the testicle and ovary. Here there can hardly be any doubt of 

 the development of muscle fibres from connective-tissue cells, however we 

 may suppose their source to be from the muscle corpuscles in the intra- 

 muscular new formation. 



Though it was formerly believed that wounds of muscles could be 

 repaired by connective-tissue alone, numerous recent observations have 

 proved the power of regeneration inherent in the tissue. The mode 

 of this new formation of muscle is a matter, however, about which much 

 difference of opinion still exi.sts. 



E. Composite Tissues. 



15. Nerve Tissue. 

 174. 



The form-elements of the nervous system (1) are structures of two 

 different kinds, namely fibres and cells, imbedded in a ground-work of con- 

 nective-tissue. The first of these, known under 

 the several names of "nerve fibres," "nerve 

 tubes," and " primitive fibres " of the nervous 

 system, make up almost exclusively the white 

 substance of the neural apparatus. The last, to 

 which the names of " nerve or ganglion cells " 

 have been given [also " ganglion corpuscles " 

 (" Ganglienkbrper ")], are found mixed up with 

 the first described elements, in the grey matter. 



The " groundwork " of connective-tissue pre- 

 sents itself in the first place in the form of a 

 highly developed fibrillated structure, more fre- 

 quently, however, as a more or less homogeneous 

 connecting substance (perineurium), or, finally, 

 as an extremely delicate tissue containing cells 

 and nuclei, as in the nervous centres. 



Nerve-fibres (fig. 296) are met with either as 

 dark-bordered threads, the medullated, or pale, 

 the non-medullated. They are simple un- 

 branched fibrils, except at their origin and 

 termination, and vary to an extraordinary extent 

 in thickness, measuring from 0'0225 down to 

 0*0018 mm. and less. Owing to their appear- 

 ance not being the same in all cases, we dis- 

 tinguish between broad or coarse fibres (a and b) of 0'0226 mm. (more 

 usually of O'Ol 13-0.0056 mm.), and. fine or narrow fibres, whose diameter 

 may fall to '0045-0 0018 mm. (c, d, e). 



Dark-edged nerve fibres consist of three parts, namely, of a very deli- 

 cate envelope of connective-tissue, the " neurilemma " or " primitive 

 sheath ;" of an albuminous portion extending down the centre, the so- 



Fig. 296. Nerve fibres from the 

 human being, a, a coarse speci- 

 men; 6, medium-sized fibre; 

 c, rf, e, finer still. 



