124 



THE HUMAN BODY. 



FIG. 54. The muscular coat of the stomach. 



have the power of shortening in the direction of their long 



axes, and so of diminishing the capacity of the cavities in 



the walls of which they lie. 



Cardiac Muscular Tissue. This con- 

 sists of flattened branched cells which unite 

 to form a network, in the interstices of 

 which blood capillaries and nerve-fibres run. 

 The cells present transverse striations, but 

 not so distinct as those of the skeletal mus- 

 cles, and are said to have no sarcolemma. 



The Chemistry of Muscular Tissue. The 

 chemical structure of the living muscular 

 fibre is unknown, since all the methods of 

 I chemical analysis at present discovered de- 

 Compose and kill it. It contains 75 per 

 cent of water; and, among other inorganic 

 constituents, phosphates and chlorides of 

 potassium, sodium, and magnesium. When 

 at rest a living muscle is feebly alkaline, but ] 

 after hard work, or when dying, this reaction 

 is reversed through the formation of sarco- 

 lactic acid (CaH^Oa). Muscles contain small 



quantities of grape sugar and glycogen, and of organic 



55-unstriped 

 muscie-ceiis. 



