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CHAPTER VII. 



ACTIVE ORGANS OF LOCOMOTION. OF MUSCLE. MUSCLE WITH 



STRIPED FIBRES. MUSCLE WITH UNSTRIPED FIBRES. MUSCULAR 



ACTION. ATTITUDES AND MOVEMENTS OF THE FRAME. 



THE principal movements of the body, and all those by which 

 locomotion is effected, are performed by means of a tissue termed 

 muscle, endowed with the power of contracting, and consisting 

 chemically of fibrine. This substance is arranged in the form of 

 unbranched fibres of definite size and structure, and which, when 

 examined under a high magnifying power, are found to be of two 

 kinds, distinguishable from one another by the presence or absence 

 of very close and minute tranverse bars or stripes. The fibres 

 of the voluntary muscles (or those whose movements can be 

 either excited or controuled by volition), as well as the fibres of the 

 heart, and some of those of the oesophagus, are striped ; while all 

 other muscles, including those of the alimentary canal, the uterus, 

 and bladder, all of which are involuntary, are unstriped. 



The elementary fibres of the voluntary muscles are connected 

 to one another by areolar tissue, and arranged in sets parallel to 

 one another. They are supplied with vessels and nerves, which lie 

 in the intervals between them ; and are attached, by their extre- 

 mities, through the medium of tendon, aponeurosis, or some form 

 of the fibrous tissue, to the parts which they are destined to move. 

 They form organs, for the most part solid and elongated, but which 

 are sometimes expanded into a membranous shape. 



The sets of fibres of the involuntary muscles, on the other hand, 

 usually cross each other at various angles, and interlace, and they 

 are always arranged as membranous organs enclosing a cavity, 

 which their contraction serves to constrict. The heart, besides being 

 independent of the will, agrees in both these anatomical characters 

 with the involuntary muscles, and is only allied to the voluntary by 

 the presence in its fibres of the transverse stripes. 



We shall commence with a description of the two forms of fibre. 



Of the Striped Fibres. The length of these is usually about that 

 of the muscle to which they belong, but occasionally they are 

 interrupted by tendinous intersections, as in the rectus abdominis 



