Page:The American Cyclopædia (1879) Volume XII.djvu/75

 MUSCLE 6T 6,718; in 1873, 7,940. It is built on a rocky bluff, and is the shipping point of an exten- sive and fertile country. Its lumber business is large, employing 500 hands. Four large saw mills in 1872 produced 30,100,000 ft. of lum- ber, 20,950,000 shingles, and 8,700,000 laths. The entire quantity handled at this point du- ring the same year embraced 63,668,000 ft. of lumber, 27,891,000 shingles, and 15,049,000 laths. There are two large pork-packing es- tablishments, three extensive flour mills, gas works, and three banking houses. The city has good public schools, a Catholic school, two daily, a semi-weekly, and three weekly news- papers, a monthly periodical, and 14 churches. Muscatine' was first settled in 1836, and was incorporated as a city in 1853. MUSCLE (Lat. musculus), the fibrous contrac- tile tissue forming the flesh of man and ani- mals, by which locomotion and the various functions of life requiring voluntary or invol- untary movements are performed. Whether elongated or enclosing a cavity, this tissue is arranged in the form of fibres, usually in bun- FIG. 1. Muscles and Tendons of the Arm and Hand. dies connected by areolar tissue, surrounded by a vascular network, and supplied with ner- vous filaments. Muscles are so arranged as to produce great velocity, extent of motion, and strength, without injuring the beauty of pro- portions, by the obliquity of their fibres to the tendons and of the last to the bones on which they act, and by the proximity of their points of insertion to the axis of motion of the joints. Muscles are attached to bone by means of ten- dons, rounded or flattened fibrous cords, white and shining, inelastic, and very resisting ; apo- neuroses or fasciae are firm, shining fibrous membranes, enveloping the muscles, giving at- tachments to their fibres, and often fixed to bones like the tendons. Muscles occupy the whole distance between the skin and bones, and take an elongated, broad, or thin form, according to the necessities of the several parts of the body ; their strength is in proportion to their length and thickness, and may be rapid- ly exhausted by continuous exertion. Muscles are called voluntary or involuntary, according as they are or are not under the control of the will ; the division is not strictly accurate, as all of the former at times contract indepen- dently of the will, and some of the latter are to a certain extent under the influence of vo- lition. The former are generally solid, as in the muscles of the trunk and limbs, and the latter hollow, as in the heart or the muscular layers surrounding cavities and canals. The voluntary and involuntary muscles are also dis- tinguished by their structure ; the former con- sisting of striped, the latter of unstriped fibres. The fibres of voluntary muscles are generally cylindrical, though more or less prismatic or many-sided, being somewhat flattened against each other. They vary in length in different muscles, and in the human subject average ^5- of an inch in diameter. Their color in man and the higher animals is ruddy, and they are elegantly marked by transverse or circu- lar striations, giving them a very characteris- tic appearance, which has led to their being distinguished by the name of striped fibres. They consist of a cylindrical or prismatic mass of contractile substance marked with the above FIG. 2. Striped Muscular Fibre, crushed at one end and breaking up into fibrillae. mentioned striations throughout its entire thickness, and containing also minute elonga- ted or oval bodies termed nuclei. Each fibre is invested by a delicate, transparent, structure- less and colorless membrane, the sarcolemma, which supports the contractile material and limits its lateral expansion. The fibres are FIG. 3. Striped Muscular Fibre, highly magnified, torn across, and showing the Sarcolemma. arranged side by side, parallel with each oth- er, and united in small groups or bundles of 100 to 200 each. These bundles are again united into larger secondary bundles, connect- ed with each other by areolar tissue, and so on ; the entire muscle being invested with an external fibrous expansion of condensed are- olar tissue, and abundantly supplied with blood vessels and nerves. The unstriped or involun- tary muscular fibres are soft, pale, flattened