MUSCULAR FIBRES. 



cxxi 



is easy to see that the muscular fibres are doubly refractive, and while the light and 

 dark parts most probably differ in certain physical and chemical properties, it is not 

 so clearly made out that the doubly refracting property is confined to the one of them. 



LXV. 



Nuclei, or muscle-corpuscles. A number of pale, finely granular, oval 

 corpuscles, resembling cell-nuclei, are found in the fibres. In mammalian 

 muscles they lie upon the inner surface of the sarcolemma, but in frogs they 

 are distributed through the substance of the fibre (fig. LXV.). These have 

 been supposed to be connected with the 

 growth and nutrition of the muscle. They 

 are obvious in the foetus some time before 

 birth, but afterwards the addition of acetic 

 acid is usually required in order to render 

 them visible. They are probably nuclei per- 

 taining to the elongated cells in which the 

 substance of the fibres is originally de- 

 veloped ; and a small amount of granular 

 matter which is not uncommonly collected 

 around them has been regarded as a remnant 

 of the formative protoplasm. Other cor- 

 puscles, mostly fusiform, but varying in 

 shape, and having the character of con- 

 nective tissue corpuscles, lie here and there 

 outside the sarcolemma, and doubtless be- 

 long to the interposed connective tissue. 



Interstitial granules. Different obser- 

 vers, and especially Kolliker, have described 

 fine granules disposed in rows between the 

 fibrils or smaller bundles of fibrils, as of 

 frequent occurrence in the muscular fibres 

 of man and animals (fig. LXVL). They 

 have been especially noted in the heart, 



and although they do not naturally show the characters of fat, it has been 

 presumed that they may by conversion give rise to the fatty degeneration 

 of muscular tissue. I must confess that I have not been able to perceive 

 these granules in healthy human voluntary muscle. 



Length and ending of the fibres. The fibres composing a muscle are of 

 limited length, not exceeding one inch and a half ; and accordingly in a long 

 fasciculus a fibre does not reach from one tendinous attachment to the other, 

 but ends with a tapering pointed extremity, invested with its sarcolemma, 

 and cohering with neighbouring fibres. Unless when either is fixed to a 

 tendon, both extremities of the fibre terminate in the way described, so 

 that it has a long fusiform shape. 



Branched fibres. Generally speaking, the fibres neither divide nor anas- 

 tomose ; but this rule is not without exception. Branched and anastomosing 

 fibres are common in the heart (fig. LXXII.) ; in the tongue of the frog the 

 muscular fibres (fig. LXVII. ) as they approach the surface divide into 

 numerous but not anastomosing branches, by which they are attached to the 

 under surface of the mucous membrane. The same thing has also been 

 seen in the tongue of man and many other animals ; and the fibres of the 

 facial muscles of mammals have been shown by Busk and Huxley to divide 

 in a similar manner where they fix themselves to the skin. 



Connection with tendons. According to Professor Kolliker, the mode of 



Fig. LXV. A FROG'S MUSCULAR 

 FIBRE TREATED WITH ACETIC 

 ACID, MAGNIFIED 350 DIAM. 

 (from Kolliker). 



The nuclei are somewhat shrunk. 

 Interstitial granules in longitudinal 

 rows, here and there, but these are 

 mostly indistinct from compression, 

 and appear as mere lines. 



