Fig. 11. Myofibril in the specific tissue (im- 

 pulse conducting system) of the steer heart. The 

 longitudinallj' arranged myofilaments are seen 

 with their various thickenings related to particu- 

 larly the Z and M bands. Mitochondria (M) and 

 microvesicles (Ve) are abundant throughout the 

 sarcoplasm. Magnification X 49 ,000 



Fig. 12. Longitudinal section through the con- 

 tractile region of the sarcoplasm of a smooth mus- 



cle cell of the mouse intestine. Fibrillar units may 

 be distinquished (arrows) and a certain longitud- 

 inal arrangement is vaguelj' indicated. In the con- 

 tractile region is always present a certain number 

 of dense, ovoid structures (0), typical for the 

 smooth muscle sarcoplasm. At the cell boundary 

 (CB) are aggregations of microvesicles (Ve). The 

 mitochondria (M) are clustered in the central por- 

 tion of the cell. Magnification X47,000 



