86 NORMAL HISTOLOGY AND ORGANOGRAPHY. 



cytoplasm is longitudinally striated, the striations 

 being due to fibrils or sarcosiyles, which are, structur- 

 ally, probably analogous to the spongioplasm. 

 Between the fibrils there is a homogeneous sub- 

 stance, the sarcoplasm, which is analogous to the 

 hyaloplasm. These cells are enclosed in a delicate 

 cement layer usually not described as a cell wall, and 

 in which a fine interlacing reticulum has recently 

 been described. The ends overlap each other and 

 are held together by a delicate cement substance. 

 Nerve-fibers from the sympathetic nervous system 

 reach the muscle cells and terminate in small gran- 

 ules upon the muscle cytoplasm. 



Nucleus 



Nucleus 



Vein. 



Fig. 52. a, Cell from smooth muscle of intestine; b, Cross section of 

 smooth muscle of intestine. 



Smooth muscle is found in the wall of the tubes of 

 the body, and invariably in thin layers, with one 

 exception the wall of the uterus where the muscle 

 may be an inch in thickness. Usually, too, this 

 muscle is laid down as an internal circular layer 

 with an externally applied and thinner longitudinal 

 layer. Plain muscle is found in the wall of the ali- 

 mentary tract, trachea and bronchi, bladder, ureter, 

 uterus, Fallopian tubes, urethra, vas deferens, 



