INVOLUNTARY MUSCULAR TISSUE 



417 



MUSCULAR MOVEMENTS 



Muscular movements are divided into voluntary and involuntary; 

 and usually there is a corresponding division of the muscles as regards 

 their minute anatomy. The latter, however, is not absolute ; for there 

 are certain involuntary actions, like the contractions of the heart or the 

 movements of deglutition, that require the rapid and vigorous contrac- 

 tion characteristic of the voluntary muscular tissue ; and here the struc- 

 ture resembles that of the voluntary muscles. 



Physiological Anatomy of the Involuntary Muscular Tissue. The 

 involuntary muscular system presents a striking contrast to the volun- 



Fig. 85. Muscular 

 fibres from the aorta of 

 the calf, X 200 (Sappey). 



i, i, fibres joined with 

 each other ; 2, 2, 2, isolated 

 fibres. 



Fig. 86. Muscular fibres from the 

 uterus of a -woman who died at the ninth 

 month of utero-gestation, X 350 (Sappey) . 



i, i, 2, short wide fibres; 3, 4, 5, 5, 

 longer and narrower fibres; 6, 6, two 

 fibres united at 7; 8, small fibres in 

 process of development.. 



Fig. 84. Muscular 

 fibres from the urinary 

 bladder of the human sub- 

 ject, x 200 (Sappey) . 



i, i, i, nuclei ; 2, 2, 2, 

 borders of some of the 

 fibres ; 3, 3, isolated fibres ; 

 4, 4, two fibres joined to- 

 gether at 5. 



tary muscles, not only in its minute anatomy and mode of action, but in 

 the arrangement of its fibres. While the voluntary muscles are almost 

 invariably attached by their extremities to movable parts, the involun- 

 tary muscles form sheets or membranes in the walls of hollow organs, 

 and by their contraction they simply modify the capacity of the cavities 

 which they surround. On account of the peculiar structure of the fibres, 

 they have been called muscular fibre-cells, smooth muscular fibres, pale 

 fibres, non-striated fibres, fusiform fibres or contractile cells. The dis- 

 tribution of these fibres to parts concerned in the organic functions, as 



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