Anatomy of Muscular System

MUSCULAR SYSTEM, ANATOMY OF (see also MUS CLE, STRUCTURE OF). Here only the voluntary muscles, under the control of the will, are considered.

The voluntary muscles form the red flesh of an animal, and are the structures by which one part of the body is moved at will upon another. Each muscle is said to have an origin and an insertion, the former being that attachment which is usually more fixed, the latter that which is more movable. This distinction, though convenient, is arbitrary, as an example will show. The pectoralis major being attached to the front of the chest and to the upper part of the arm bone its contraction draws the arm towards the chest, whereas, when, in climbing a tree, the hand grasps a branch above, contraction will draw the chest towards the arm. Generally, a muscle is partly fleshy and partly tendinous; the fleshy con tractile part is attached at one or both ends to cords or sheets of white fibrous tissue, which in some cases pass round pullies and so change the direction of the muscle's action. The other end of these cords or tendons is usually attached to the periosteum of bones, with which it blends. In some cases, when a tendon passes round a bony pulley, a sesamoid bone is developed in it which diminishes the effects of friction. A good example of this is the patella in the tendon of the rectus femoris (fig. 1).

Every muscle is supplied with blood vessels and lymphatics (fig. 1), and with one or more nerves. The nerve supply is very important both from a medical and a morphological point of view. The attachments are also important, as determining the action of the muscle. This action cannot be understood by refer ence to the dead body alone, for every movement expresses the balanced contractions of numer ous muscles. (See C. E. Beevor, Croonian Lectures for 1903, Lon don, 1904.) Muscles may be fusiform, as in fig. I, conical, riband-like, or flattened into triangular or quad rilateral sheets. They may also be attached to skin, cartilage or fascia instead of to bone, while certain muscles surround open ings which they constrict and are called sphincters. The names of the muscles have gradually grown up, and no settled plan has been used in giving them. The German anatomists at the Basle confer ence lately proposed a uniform Latin and Greek nomenclature, which, though not altogether satisfactory, is gaining ground on the European continent. As there are some four hundred muscles

on each side of the body it will be impossible here to attempt more than a mere sketch ; for the details the anatomical textbooks must be consulted.

Muscles of the Head and Face (P1. I.–i).

The scalp is moved by a large flat muscle called the occipito-frontalis, which has two muscular bellies, the occipitalis and frontalis, and an inter- , vening epicranial aponeurosis; this muscle moves the scalp and causes the transverse wrinkles in the forehead. The anterior, pos terior and superior auricular muscles are present but are almost functionless in man. The orbicularis palpebrarum forms a sphinc ter round the eyelids, which it closes, though there is little doubt that parts of the muscle can act separately and cause various ex pressions. The side of the nose has several muscles, the actions of which are indicated by their names ; they are the compressor, two dilatores and the depressor alae nasi, while the levator labii superi oris et alae nasi sometimes goes to the nose. Raising the upper lip, in addition to the last named, are the levator labii superioris pro prius and the levator anguli oris, while the zygonzaticus major draws the angle of the mouth outward. The lower lip is depressed by the depressor labii inf erioris and depressor anguli oris, while the orbicularis oris acts as a sphincter to the mouth. The buccinator muscle in the substance of the cheeks rises from the upper and lower jaws and runs forward to blend with the orbicularis oris. All the foregoing are known as muscles of expression and all are sup plied by the seventh or facial nerve. The temporal muscle at the side of the cranium (Pl. 1.-3) and the masseter (Pl. I.-2), which rises from the zygoma, close the mouth, since both are inserted into the ramus of the mandible; while, rising from the pterygoid plates, are the external and internal pterygoid muscles (Pl. 1.-3), the former of which pulls forward the condyle, and so the whole mandible, while the latter helps to close the mouth by acting on the angle of the lower jaw. This group of muscles forms the mas ticatory set, all of which are supplied by the third division of the fifth nerve. For the muscles of the orbit, see EYE; for those of the soft palate and pharynx, see PHARYNX; and for those of the tongue, see TONGUE.