MUSCLE

n. Mu 'l. Gr.MSs. Lat., musculus. Fr.,m. Ger., Muskel, Muskelgewebe. An aggregation of muscular (sarcous) ti ue, which is the ti ue in the animal body characterized physiologically by its power of contracting in one direction and thus giving rise to definite movements. The structural elements are usually much greater in length than in breadth, and hence are mostly designated as muscular fibres. These may be apparently homogeneous and in spindle-shaped cells or fibres (unstriated, smooth, or involuntary m.1, or the substance composing the elements may appear to be composed of alternating segments of light and dark material (striated m.). The striated elements of the vascular system (cardiac m.) are usually quite short, branched, and in Mammal i a anastomosing. The skeletal m's are composed of elements much greater in length than in breadth. Only in a few cases do the fibres branch or anastomose. The fibres rarely exceed 40 to 60 mm. in length, and in m's of considerable length the fibres continually terminate and originate, but in short m's they extend from tendon to tendon. Smooth or unstriated m. is mostly in sheets or isolated bundles, and in connection with the organs of vegetative life. It is mostly involuntary, the m. of accommodation forming an apparent exception. Cardiac m. is wholly involuntary, while the ordinary skeletal striated m. is voluntary. That in the oesophagus is an exception, and the m's of respiration are only partially voluntary. [J, 30, 55, 175; S. P. Gage, " Microscope," viii, pp. 225, 257.] For m's with special generic names, such as abductor, adductor, etc., see under those names. Acce ory m's. See under AccE oR irs. Alar m's, Alary m's. In some insects, m's atE. he: K. ell: O, go; I, die: I*, in: N, in; N, tank; [s. 42]