MUSCULAR ACTION 



377 



SMOOTH MUSCLE is made up of fusiform anisotropic cells ranging in 

 length from about 0.040 to 0.225 mm., and in width from 0.004 to 

 0.008 mm. They reach their known maximum size in the uterus in its 

 pregnant state, where they are often more than double the maximum given 

 above. The reticulated nucleus is elliptical and is placed nearly in the 

 middle of the cell. Striations (myoids ?) are clearly to be made out run- 

 ning the entire length of the cell. Those about the periphery of the cyto- 



FIG. 230 



I- 



Smooth muscle-fibers of the uterus: a, from a virgin; 6, from a pregnant woman 



(Bumm.) 



plasm are relatively coarse and straight, while within they are finer and 

 constitute a distinct reticulum. Between the fibrils is the homogeneous 

 and transparent sarcoplasm. The cells are collected together in spindle- 

 shaped bundles, each bundle being enclosed in a delicate fenestrated 

 membrane (as is also each cell) called its sarcolemma. The meaning 

 of the oval openings in this membranous bundle-covering is not yet clear. 

 Several histologists have described fine protoplasmic bridges connecting 

 the sarcoplasm of the cells in the bundle, but these have been declared 



