COMPOUND TUBULAR TISSUES. 



35 



merely those of very minute size, which, admitting only a single 

 row of blood corpuscles, do not contain a sufficient amount of colour- 

 ing matter to affect the lij 



[ht transmitted through them. 



COMPOUND TUBULAR TISSUES. 



Examples of these are seen in the muscular and nervous tissues, 

 in which, after tubes have been formed by the coalescence of the cells, 

 their interiors are filled up with a secondary deposit. The functions 

 of these two tissues are widely different. The muscular is that by 

 which all the sensible movements of the body are effected. The 

 nervous is that by which sensations are received ; and by which the 

 instincts, emotions, or volitions excited by these sensations, act upon 

 the muscles. 



The ultimate structure of these two tissues is alike ; both consist 

 of tubes formed by the coalescence of cells. The difference between 

 them exists in the nature of the internal deposit. 



There are two forms of muscular tissue, — in one the ultimate fibrils 

 are marked by transverse stri83, or bands ; in the other, they are 

 plain, or unstriped. The former, or the striped fibres, are found in 

 all the voluntary muscles, or, as they are sometimes called, the mus- 

 cles of animal life. The latter are seen in those muscles which are 

 concerned in the organic or vegetative functions. They are not so 

 readily called into action through the agency of the nervous system, 

 as the striped muscles, but are more readily excited by stimuli applied 

 directly to themselves. 



An ordinary muscle is seen, even by the naked eye, to consist of 

 bundles of fibres, arranged with great regularity, in the direction in 

 which the muscle is to act. These fibres are arranged m fasciculi, 

 or bundles, connected together by means of areolar tissue. Each 

 fibre presents two sets of markings, or striae, one set longitudinal, 

 the other transverse. By close examination the individual fibre may 

 be separated into fib- 



rillee by the splitting of Fig. 9.* 



its contents in a longi- 

 tudinal direction. (Fig. 

 9.) These fibrilloe pre- 

 sent a headed appear- 

 ance, caused by the pe- 

 culiar arrangement of 

 the contents of the tube. 



It frequently happens, 

 that when force is ap- 

 plied to a fibre, its con- 

 tents separate in the 

 direction of the trans- 



* 1. Longitudinal cleavage. 2, 3, 

 disk showing the sarcous elements, 

 ments. 



. Transverse cleavage forming disks. 5. A detached 

 7, b. Separated fibrillae showing the beaded enlarge. 



