MUSCLE MOVEMENTS 



another, forming a small bundle, and the several bundles, which 

 may run parallel to each other, but often cross and interlace, are 

 bound together by fine connective tissue. 



Cardiac Muscular Tissue. The muscular tissue of 

 which the heart consists differs from both striated and plain 

 muscular tissue. The individual fibres are like plain muscular 

 fibres in containing a single oval nucleus and in being devoid 

 .of sarcolemma, but are short and thick, not 

 long and narrow. They are, moreover, faintly 

 striated transversely by light and dark bands. 

 They are arranged end to end in columns, and 

 each fibre or fibre cell in the column has one 

 or two short thick branches by which it is 

 united to the branches of the cells of neigh- 

 bouring columns. The muscle cells are bound 

 together in this way to form sheets or bundles 

 of muscular tissue, which interlace largely, and 

 the bundles are bound together by a little con- 

 nective tissue in which blood-vessels and nerves 

 lie. 



Muscular Movement 



.... FIG. 33. Two car- 



A movement of a limb is produced by one diac muscle fibres. 



or more muscles drawing their ends nearer to- Mt nucleus; /.line of 



gether, and in this way moving one or both of junction of the two 



the bones to which the ends are attached. A flbrcs ; /; P rocess 



... . . which joined an- 



muscle draws its ends nearer together by other fibre< 

 becoming for the time shorter, and in doing so 

 becomes thicker or larger in the middle, for the muscle does 

 not become smaller, or change its bulk. When a muscle has 

 drawn its ends nearer together it is said to be contracted ; 

 \\hcn it has again resumed its original length and shape it is 

 said to be relaxed. The contraction of a muscle is caused by 

 the contraction of the individual muscular fibres of which it is 

 composed, each fibre shortening in length and becoming pro- 

 portionately thicker, the sum total of the contraction of these, 

 taking place at the same time, making up the contraction of 

 the whole muscle. 



Kill a frog by cutting off the head as low down as possible. 

 Strip the skin off the hind legs. This is best done by cutting 



