ORGANISATION AND STRUCTURE OF MUSCLE 



29 



fibrils, which by proper methods can again be split up into 

 the true elementary fibrils. As in the uninuclear muscle- 

 cells, the multinuclear muscle-fibres fall in the main into two 

 distinct forms or types of " muscle-columns." These are either, 

 as in many invertebrate muscles, flat band-like bundles, composed 

 of a single row, or some few rows, of fibrils only, or (as is more 

 common) the bundles appear to be cylindrical or prism-shaped, 

 i.e. circular or polygonal in cross-section. 



When, as in the majority of cases, the prismatic "muscle- 

 columns " are separated by a comparatively insignificant mass of 

 " interstitial substance," a mosaic of polygonal areas appears in 

 transverse section as first described by Cohnheim ; whence, 

 therefore, the name of CohnJt din's Arece (Fig. 18, a, 5). 



FIG. IS. a, Transverse section of muscle-fibre of Rabbit (bundles of fibrils dark, sarcoplasm clear). 

 (Kolliker.) //, Transverse section of muscle-fibre of Frog, showing on the left cross-sections 

 of the fibrils. (Schiefferdecker.) 



It is questionable whether the sarcoplasm that surrounds the 

 muscle-columns penetrates also between the individual fibrils : 

 Eollett disputes it ; Kolliker assumes a minute amount of inter- 

 stitial matter, identical with the sarcoplasm it can only be 

 identified under a very high power, and forms an investing sheath 

 along the entire length of each fibril. 



From this last point of view each muscle-fibre must be re- 

 garded as a bundle of fibrils which are held together by an 

 uneven accumulation of intermediary substance. " According as 

 this accumulation is more or less abundant, the muscle-columns 

 are more or less well defined, larger or smaller " (Kolliker). 



The comparative proportion of the two chief constituents of a 

 muscle-fibre, i.e. the fibrils (Kuhne's rhabdia) and the sarcoplasm, 

 varies, as we have said, in different animals, and in different 



