HISTOLOGY OF MUSCLE. 



439 



in them we find a thin, elongated form of muscle cell. In the 

 heart a forcible and quick contraction takes place, which, how- 

 ever, is slow when compared with the 

 sudden jerk of a single spasm of a skeletal IG< ^7. 



muscle, and we find its texture is different, 

 being a form intermediate between the 

 slow-contracting smooth muscle and the 

 quick-contracting striated skeletal muscle. 



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, 

 nonstriated 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- 

 tile protoplasmic cells, and have so far 

 retained the typical form as to be easily 

 recognizable as cells when separated one 



from the other. These cells are more or 



. protoplasm of the cell 



less elongated, flattened, homogeneous ele- and nuc i eus . 



ments with a single, long, rod-like nucleus 



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



Muscle cells, showing 

 different condition of the 



