34- 



] onrnal of Agriculture. 



[8 June, 1907. 



name implies that they are under the control of the will. They are set 

 into activity solely by nerve impulses which come to them from the 

 central nervous system and are more dependent on the central nervous 

 system than any other form of tissue, for, if the nerve supplying the 

 muscle be cut and not allowed to heal, the muscle rapidly undergoes 

 atrophv and dies. The third name informs us that such muscles are 

 attached, at least by one end, to bone and by their contraction can, in 

 most cases, make certain bones to move with respect to each other. A 

 glance at the illustration on page 344 will make this clear. Here two 

 muscles are shown, the tibialis anticus and the gastroaiemius, which have 

 each a double bony attachment. In each of these types there is a broad 



Ri'-.illhiiri 







Pig ^o. — Part of a contractile cell of skeletal muscle. The cross stripes are 

 due to the rows of prismatic bodies. A wave of contraction is seen passing along 



the cell. (After Schafer.). 



origin and a narrow insertion by means of a tendon or sinew, but these 

 features are by no means universal amongst muscles. Now if the gas- 

 trocnemius alone were to contract, the calcaneum would be drawn nearer to 

 the femur, in other words the hock would be opened out or extended, and 

 the stifle somewhat flexed. If the tibialis anticus alone were to contract, 

 the hock would be flexed. With respect to the hock these two muscles 

 are therefore antagonistic in their action and similar arrangements will 

 be found if we examine any other joint, one set of muscles being extensor 



