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STUDIES IN ADVANCED PHYSIOLOGY. 



six-hundredth of an inch in length and very narrow, re- 

 sembling elongated spindles. They seem to show a very 

 faint longitudinal striation, and possess near their center a 

 very evident nucleus. It is impossible to establish a cell 

 wall, like a sarcolemma, though probably enveloped with a 

 dark, denser layer. They are never joined to tendons, but 

 are cemented together to form sheets of muscle. Bach 

 muscle fibre is probably supplied with its own nerve; but 

 in this case the nerve has no end plate, but after encircling 

 the fibre once or twice ends abruptly in the nucleus. They 

 are not very vascular, and in cross-sections of involuntary 

 muscular tissue, the capillaries of which have been injected 

 so as to make them readily visible, there may be as many 

 as twenty-five or thirty rows of plain cells between neigh- 

 boring capillaries. 



II 



Fig. 64. INVOLUNTARY MUSCLE FIBRE CELLS, FROM A HUMAN ARTERY. (After Kb'lliker.) 

 a, nucleus; ft, a fibre treated with acetic acid to render it more transparent. 



These cells have the power of shortening their long 

 axis, but do not possess to any such extent as the volun- 

 tary muscles the ability to contract quickly or energetically. 

 They are peculiarly well adapted to the visceral organs, 

 where it is evident that the movement ought to be very 

 slow, gradual and measured. Examples of this tissue may 

 be found in the walls of the stomach and intestines, in the 



