MUSCLE. 



[ 526 ] 



MUSCLE. 



rous very slender parallel longitudinal mus- 

 cle-rods (PI. 22. fig. 36 e). These extend at 

 either end into the adjacent white bands, 

 terminating in knotted ends; forming a row, 

 running transversely across each white 

 band. 



When muscular fibres are examined by 

 polarized light, the sarcous elements are 

 seen to be anisotropous or doubly refractive, 

 while the intermediate substance is iso- 

 tropous. 



They are also well supplied with nerves ; 

 these mostly (always, Beale) terminate in a 

 plexus of looped branches (fig. 603). 



Fig. 603. 



Termination of the branches of a nerve in a portion 

 of the omohyoideus muscle, treated with caustic soda : 

 a, meshes of the terminal plexus ; 6, loops ; c, muscular 

 fibres. 



Magnified 350 diameters. 



In the Insects and Reptiles the nerves 

 terminate in granular nucleated swellings, 

 spread over the muscular bundles; their 

 sheaths becoming continuous with the sar- 

 colemma, the nerve-fibres branching off in 

 various directions. 



Muscle undergoes important changes in 

 disease. Wounds are filled up with connec- 

 tive or tendinous tissue. In atrophy and 

 fatty degeneration, the bundles become 

 smaller, softer, more readily broken up, the 

 transverse striae and fibrillae indistinct, or 



apparently absent, and contain yellowish or 

 brown pigment-granules, with more or less 

 numerous globules of fat (PI. 38. fig. 14 a), 

 and sometimes a large number of nuclei or 

 small cells. 



Muscular fibres with nerve-ends from Lacerfa viridii. 

 A. Been in profile : P P, the terminal nerve expansion 

 or plate ; SS, its support or base, consisting of a granu- 

 lar mass with nuclei. B. The same, seen in a perfectly 

 fresh muscular fibre. 



The interfascicular connective tissue is also 

 sometimes increased in amount, and fatty 

 tissues developed in it; or the muscular sub- 

 stance is partially absorbed, and the sarco- 

 lemma contracting gives the bundles a 

 moniliform appearance (PI. 38. fig. 146). 

 In tetanus, the fibres become varicose and 

 often ruptured, and the striae closer. 



The muscular tissue of the lower Verte- 

 brata and some of the Invertebrata agrees 

 essentially in structure with that of man ; 

 but the sarcolemma is often much thicker, 

 the fibrillse larger, and the nuclei contained 

 within the substance of the bundles, and 

 sometimes arranged in regular linear series. 

 The margins of the bundles are also some- 

 times uneven, and rounded at regular inter- 

 vals (PI. 22. fig. 35), giving the appearance 

 of their being surrounded by fibres. 



In many of the lower members of the In- 

 vertebrata, although the substance of the 

 body is voluntarily contractile, no trace of 

 fibres or bundles can be detected. 



The so-called muscle-corpuscles are placed 

 in the interior of the fibre in the muscles 

 of the heart ; and they are to be met with in 

 Amphibia, Fishes, and Birds in the same 

 position. 



