Buckmaster's Elements of animal physiology / by John Angell.

  • Angell, John
Date:
1866
Catalogue details

Licence: Public Domain Mark

Credit: Buckmaster's Elements of animal physiology / by John Angell. Source: Wellcome Collection.

    295/384 (page 283)
    Flexors and Extensors (from ^.,jlecto,\ bend, and ex, out, and tendo, I stretch).—Those muscles which bend a limb, as the biceps muscle in front of the arm (see 3, Fig. 67), are termed flexors. Those muscles which straighten or extend the limbs, as the triceps muscle at the back of the arm (see i. Fig. 67), are termed extensors. A flexor, with its corresponding extensor, constitute a pair of antagonist muscles. The Orbicular and Sphincter Muscles (from L., orbis, a circle, and Gr., sphiggo, 1 contract) are circular, oval, or ring- shaped muscles, which surround and by their contraction close certain apertures or orifices, as the orbicularis oris, or circular muscle which surrounds and closes the lips; the orbicularis palpebrarum, which surrounds the orbit and eyelids, and by its contraction closes the eyelids; and the sphincter ani, which surrounds and closes the terminal aperture of the rectum. Abductor, Adductor, and Levator Muscles (from L., ab, from ; ad, to ; and duco, I draw).—Those muscles which by their contraction draw one organ or part frosn another are termed abductors, as the abductor of the thumb. Those muscles which pull the organ or part inward are termed adductors, as the adductor occuli, which moves the eyeball inwards. Those muscles which raise or hft up the parts to which they are attached are termed levator muscles, as the levatores costarum. (See Fig. 31.) Names of the Muscles.—In addition to the classes of muscles already given, muscles are named—(i) according to their shape, as the deltoid, denticulated, rectus, rho7nboidal, square, triangular, and oblique muscles; (2) according to the parts of the body to which they are attached, as the abdominal, brachial, cervical, crural, dorsal, facial, pectoral, pelvic, and thoracic muscles 5(3) from their divisions, as the biceps and triceps muscles. Origin and Insertion.—The end of the muscle which is attached to the immoveable bone is termed its origin, and that extremity which is attached to the moveable bone its insertion ; the intermediate part of the muscle, when full and thick, is termed its belly. (See Fig. 67.) Voluntary and Involuntary Muscles (from L., volo, I will, and fw, not).—The muscles of pre- hension and locomotion, &c., act according to and under the direction of the will, and are therefore