442 MANUAL OP PHYSIOLOGY. 



FIG. 177. 'ever, is slow when compared with the 



sudden jerk of a single spasm of a skeletal 

 muscle, and we find its texture is different, 

 being a form intermediate between the 

 slow-contracting, smooth muscle and the 

 quick-contracting, striated skeletal mus- 

 cle. . 



By borrowing examples from the lower 

 animals, this parallelism of structural dif- 

 ferentiation and increase of functional 

 energy can be more perfectly demon- 

 strated, and we can make out a gradual 

 scale of increasingly rapid motion cor- 

 responding with greater complexity of 

 structure. 



The contractile tissues of the human 

 body show many varieties both of func- 

 tional and structural differentiation. 



HISTOLOGY OF MUSCLE. 



The term muscle includes the textures 

 in which the protoplasm is specially dif- 

 ferentiated for purposes of contraction. 



The muscle tissues of the higher ani- 

 mals may be divided into two classes : 1, 

 non-striated or smooth, and 2, striated, in 

 which again there are some slight varia- 

 tions. 



The unstriated muscle tissue is that in 

 which the elements are most like contrac- 

 Muscie ceils, showing differ- ti i e pro t plasmic cells, and have so far 



ent condition of the proto- * A 



plasm of the cell and nucleus, retained the typical form as to be easily 

 recognizable as cells when separated one 



from the other. These cells are more or less elongated, flattened, 

 homogeneous elements, with a single, long, rod-like nucleus and 

 no cell wall. They are tightly cemented together by a tough, 

 elastic substance, so that their tapering extremities fit closely 



