n] 



HISTOLOGY 



21 



called skeletal muscles, or, as already mentioned, voluntary 

 muscles. 



Cardiac or heart muscle also shows a transverse striation, but 

 the cells are short and squat, and have branches which unite 



Fig. 15. Cardiac muscle (from 

 Schafer). 



Fig. 16. Unstriated muscle 

 fibres from bladder of frog . 

 (highly magnified). Note the 

 spindle shaped nuclei and 

 the longitudinal fibrillation. 



them with those of neighbouring fibres, and there is no sarco- 

 lemma. Each cell has a central nucleus. 



Involuntari/, non-striated, smooth, or plain muscle is devoid of 

 striations. The cells are usually fairly long and taper at both 

 ends. The nucleus which is elongated is situated centrall}'. 

 Connective tissue is present (as in the case of heart muscle) 

 but there does not appear to be a true sarcolemma. Smooth 

 muscle occurs in the walls of the alimentary canal, the trachea, 

 the urinary V)ladtler, the uterus, and various other organs, the 

 movements of which are not under the control of the will. It is 

 well developed also in the middle coats of arteries, veins, and 



