446 MOVEMENTS. 



sion of the muscles as regards their minute anatomy. The 

 latter, however, is not absolute ; for there are certain invol- 

 untary functions, like the action of the heart or the move- 

 ments of deglutition, that require the rapid, vigorous con- 

 traction characteristic of the voluntary muscular tissue ; and 

 here we do not find the structure of the involuntary mus- 

 cles. With a few exceptions, however, the anatomical 

 division of the muscular tissue into voluntary and involun- 

 tary is sufficiently distinct. 



Physiological Anatomy of the Involuntary Muscles. 

 We have so often described this tissue, as it is found in the 

 vascular system, the digestive organs, skin, and other situ- 

 ations, that it will not be necessary, in this connection, 

 to give more than a sketch of its structure and mode of 

 action. 



The involuntary muscular system presents a striking 

 contrast to the voluntary 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 two extremities to movable parts, the in- 

 voluntary muscles form sheets or membranes in the walls of 

 hollow organs, and by their contraction simply modify the 

 capacity of the cavities which they enclose. 



Various names have been given to this tissue to denote 

 its distribution, mode of action, or structure. The name 

 involuntary muscle indicates that its contraction is not 

 under the control of the will; and this is the fact, these 

 muscles being chiefly animated by the sympathetic system 

 of nerves, while the voluntary muscles are supplied mainly 

 from the cerebro-spinal system. On account of the peculiar 

 structure of these fibres, they have been called muscular 

 fibre-cells, smooth muscular fibres, pale fibres, non-striated 

 fibres, fusiform fibres, and contractile cells. The distribu- 

 tion of these fibres to parts concerned in the organic or 

 vegetative functions, as the alimentary canal, has given 



