MUSCLE TISSUE 



49 



the muscle fibre, like the protoplasm of the cells in general, consists of a network 

 of close and very fine fibres, the spongioplasm, and of an intermediate homogeneous 

 fluid substance, the hyaloplasm. The former is contractile and elastic, the latter is 

 purely passive. In muscle fibres the spongioplasm is regularly arranged (Fig. 49, A). 

 It consists of parallej. filaments, which run longitudinally and are bound by transverse 

 filaments at regular intervals in a plane at right angles to the longitudinal axis. 

 A transverse section lying in such a plane would form a plate with reticularly 

 arranged filaments and hyaloplasm between them (Fig. 49, B}. There are no 



FIG. 48. Transversely striated 

 muscle fibre, after Gegenoauer. 



FIG. 49. Transversely striated muscle fibre of 

 an Arthropod, after Van Gehuchten. A, Lateral 

 view. B, In transverse section. 



transverse connections between the longitudinal filaments, except at these regular 

 intervals, so that on a transverse section of the fibre made at any other part of it 

 only the transverse section of the longitudinal filaments would be seen. It is clear 

 how, by such an arrangement of the finer portions, the transversely and longitudin- 

 ally striated appearance of the fibre could be produced. There are weighty objec- 

 tions, however, to these views of Van Gehuchten. 



The muscle fibres contract in response to stimuli transmitted to 

 them by the motor nerve fibres. They therefore always stand in con- 

 nection with the ends of such fibres in a manner which cannot here 

 be further described. 



Muscle fibres joined together by connective tissue unite to form 

 bundles, bands, or tubes. These again can be united in layers or in 

 thick muscle strands. 



Muscle fibres, smooth as well as striated, arise, even in many higher 

 Metazoa, out of epithelium ; in many of these, however, the muscle- 

 forming cells (Myoblasts) are descendants of cells which at an early 

 stage of their development sank below the level of the epithelium to 

 which they belonged. Both kinds of formation may occur in the same 

 animal. 



VOL. 



IB *4^v 

 Of THE T r\ 



UNIVERSITY) 



.llu 



