THE STRUCTUKE OF VOLUNTARY MUSCLE 



183 



than they were before. That there is no true reversal of the striae is shown by exam- 

 ining the muscle by polarised light, the two substances, isotropous and anisotropous, 

 retaining their relative positions. 



Every skeletal muscle is connected with the central nervous system 

 by nerve fibres, some conveying impressions from the muscle to the centre, 

 the others acting as the path of the motor impulses from the centre to the 

 muscle. These latter the motor nerves end in the muscular fibre itself, 

 by means of a special end-organ the motor end-plate. The neurilemma 

 of the nerve fibre, becomes continuous with the sarcolemma, the medullary 

 sheath ends suddenly, while the axis cylinder ramifies in a mass of un- 

 Eerentiated protoplasm, containing nuclei, and lying in contact with the 



Crural is 

 Add. magn.' 



Tib ant. long. 



Sartorius 



Add. magn. 

 Gracilis 



Tendo AchilHs 



FIG. 41. Muscles of hinder extremity of frog. (After ECKEB.) 



mtractile substance of the muscle immediately under the sarcolemma 

 (Fig. 40). This mass of protoplasm is known as the * sole plate.' It is not 

 marked in all animals. Thus in the frog the axis cylinder ends in a series of 

 branches at right angles to one another, distributed over a considerable length 

 of the muscle fibre. The sole plate in this case seems to be limited to scat- 

 tered nuclei lying in close contact with the terminal branches of the nerve 

 fibre. So far as we can tell at present, the ultimate ramifications of the 

 axis cylinder end freely and do not enter into organic connection with the 

 contractile substance itself. 



