MUSCLES AND PHENOMENA OK CONTRACTION. 123 



walls of the arteries, around the finer divisions of the bron- 

 chial tubes, and in numerous other places. 



Cardiac Muscle. 



The third kind of muscular tissue occurs only in the 

 heart. The fibres in this case are cross-striped, very simi- 

 lar to the voluntary. They are not quite as wide as the 

 voluntary, but are very much shorter, a typical heart fibre 

 being usually only about twice as long as it is wide. It 

 possesses near its center an evident nucleus, in which no 

 doubt, the nerve ends. There are no tendons, but the 

 cells are cemented together in bands of fibres. Very fre- 

 quently these cells are branched, a property possessed by 

 neither of the other kinds of fibres. Because of this cross- 

 striation and its size it is evident that it is an intermediate 



Fig. 65. Six CARDIAC MUSCLE FIBRES. (After Schafer.) 

 b, c, showing branching of cells. 



kind of muscle possessing some of the properties of both, 

 and therefore peculiarly well adapted for use in the heart, 

 where much greater energy of contraction is desired than 

 in the ordinary involuntary muscles. 



The Chemistry of Muscle. 



The muscles possess about seventy-five per cent, of 

 water, traces of various mineral salts, bits of grape sugar, 



