The Muscles and Fasciae are described conjointly, in order that the student may consider the arrangement of the latter in his dissection of the former. It is rare for the student of anatomy in this country to have the opportunity of dissecting the fasciae separately; and it is from this reason, as well as from the close connexion that exists between the muscles and their investing aponeuroses, that they are considered together. Some general observations are first made on the anatomy of the muscles and fasciae, the special description being given in connexion with the different regions.

The Muscles are the active organs of locomotion. They are formed of bundles of reddish fibres, consisting chemically of fibrine, and endowed with the property of contractility.

Muscle is of a deep red colour, the intensity of which varies considerably with the age and health of the individual. It is composed of bundles of parallel fibres, placed side by side, and connected together by a delicate web of areolar tissue. Each fasciculus consists of numerous smaller bundles, and these of single fibres, which, from their minute size and comparatively isolated appearance, have been called ultimate fibres. Two kinds of ultimate muscular fibre are found in the animal body, viz., that of voluntary or animal life, and that of involuntary or organic life. The ultimate fibre of animal life is capable of being either excited or controlled by the efforts of the will, and is characterised, on microscopic examination, by its size, its uniform calibre, and the presence of minute transverse bars, which are situated at short and regular distances throughout its whole extent. Of such is composed the muscular tissue of the trunk and limbs; the fibres of the heart, and some of those of the oesophagus: the muscles of the internal ear, and those of the urethra, present a similar structure, although they are not capable of being acted upon by the will. Involuntary muscular fibre is entirely withdrawn from the influence of volition, and is characterised, on microscopic examination, by the ultimate fibrils being homogeneous in structure, of smaller size than those of iinimal life, flattened, and unstriped; of such the muscles of the digestive canal, the bladder, and uterus are composed.

Each muscle is invested externally by a thin cellular layer, forming what is called its sheath, which not only covers its outer surface, but penetrates into its interior in the intervals between the fasciculi, surrounding these, and serving as a bond of connection between them.

The voluntary muscular fibres terminate at either extremity in fibrous tissue, the separate fibrillse of which being, in some cases, aggregated together, form a rounded or flattened fibrous cord or tendon; in the flat muscles, the separate fibres are arranged in flattened membranous laminae, termed aponeuroses; and it is in one or other of these forms, that nearly every muscle is attached to the part which it is destined to move.

The involuntary muscular fibres, on the contrary, form a dense interlacement, crossing each other at various angles, forming a layer of variable thickness, which usually circumscribes the wall of some cavity, which, by its contraction, it constricts.

Muscles vary considerably in their form. In the limbs, they are of considerable length, especially the more superficial ones, the deep ones being generally broad; they surround the bones, and form an important protection to the various joints. In the trunk, they we broad, flattened, and expanded, forming the parietes of the cavities which they enclose; hence the reason of the terms, long, broad, short, etc., used in the description of a muscle.

There is considerable variation in the arrangement of the fibres of certain muscles, in relation to the tendon to which they are attached. In some, the fibres are arranged longitudinally, and terminate at either end in a narrow tendon, so that the muscle is broad at the centre, and narrowed at either extremity: such a muscle is said to be fusiform in shape, as the Rectus femoris. If the fibres converge, like the plumes of a pen, to one side of a tendon, which runs the entire length of the muscle, it is said to be penniform, as the Peronei; or, if they converge to both sides of a tendon, they are called bipenniform, as the Rectus femoris; if they converge from a broad surface to a narrow tendinous point, they are then said to be radiated, as the Temporal and Glutei muscles.

Their size presents considerable variation: the Gastrocnemius forms the chief bulk of the back of the leg, and the fibres of the Sartorius are nearly two feet in length, whilst the Stapedius, a small muscle of the internal ear, weighs about a grain, and its fibres are not more than two lines in length. In each case, however, they are admirably adapted to execute the various movements they are required to perform.

The names applied to the various muscles have been derived: I, from their situation, as the Tibialis, Radial i?, Ulnaris, Peroneus; 2, from their direction, as the Rectus abdominis, Obliqui capitis, Transversalis; 3, from their uses, as Flexors, Extensors, Abductors, etc.; 4, from their shape, as the Deltoid, Trapezius, Rhom-boideus; 5, from the number of their divisions, as the Biceps (from having two heads), the Triceps (from having three heads); 6, from their points of attachment, as the Sterno-cleido-mastoid, Sterno-hyoid, Sterno-thyroid.

In the description of a muscle, the term origin is meant to imply its more fixed or central attachment; and the term insertion, the moveable point upon which the force of the muscle is directed: this holds true, however, for only a very small number of muscles, such as those of the face, which are attached by one extremity to the bone, and by the other to the moveable integument; in the greater number, the muscle can be made to act from either extremity.

In the dissection of the muscles, the student should pay especial attention to the exact origin, insertion, and actions of each, and its more important relations with surrounding parts. An accurate knowledge of the points of attachment of the muscles is of great importance in the determination of their action. By a knowledge of the action of the muscles, the surgeon is able at once to explain the causes of displacement in the various forms of fracture, or the causes which produce distortion in various forms of deformities, and, consequently, to adopt appropriate treatment in each case. The relations, also, of some of the muscles especially those in immediate apposition with the larger blood-vessels; and the surface-markings they produce should be especially remembered, as they form most useful guides to the surgeon in the application of a ligature to these vessels.

The Fascias (fascia, a bandage) are fibro-areolar or aponeurotic laminae, of variable thickness and strength, found in all regions of the body, investing the softer and more delicate organs. The fasciae have been subdivided, from the structure which they present, into two groups, fibro-areolar or superficial fasciae, and aponeurotic or deep fasciae.

The fibro-areolar fascia is found immediately beneath the integument over almost the entire surface of the body, and is generally known as the superficial fascia. It connects the skin with the deep or aponeurotic fascia, and consists of fibro-areolar tissue, containing in its meshes pellicles of fat in varying quantity. In the eyelids and scrotum, where adipose tissue is never deposited, this tissue is very liable to serous infiltration. This fascia varies in thickness in different parts of the body: in the groin it is so thick as to be capable of being subdivided into several laminae, but in the palms of the hands it is of extreme thinness, and intimately adherent to the integument. The superficial fascia is capable of separation into two or more layers, between which are found the superficial vessels and nerves, and superficial lymphatic glands; as the superficial epigastric vessels in the abdominal region, the radial and ulnar veins in the forearm, the saphenous veins in the leg and thigh, as well as in certain situations cutaneous muscles, as the Platysma myoides in the neck, Orbicularis palpebrarum around the eyelids. It is most distinct at the lower part of the abdomen, the scrotum, perinseum, and in the extremities; is very thin in those regions where muscular fibres are inserted into the integument, as on the side of the neck, the face, and around the margin of the anus, and almost entirely wanting in the palms of the hands and soles of the feet, where the integument is adherent to the subjacent aponeurosis. The superficial fascia connects the skin to the subjacent parts, serves as a soft nidus, for the passage of vessels and nerves to the integuments, and retains the warmth of the body from the adipose tissue contained in its areolae, being a bad conductor of caloric.

The aponeurotic or deep fascia is a dense inelastic and unyielding fibrous membrane, forming sheaths for the muscles, and affording them broad surfaces for attachment, it consists of shining tendinous fibres, placed parallel with one another, and connected together by other fibres disposed in a reticular manner. It is usually exposed on the removal of the superficial fascia, forming a strong investment, which not only binds down collectively the muscles in each region, but gives a separate sheath to each, as well as to the vessels and nerves. The fasciae are thick in unprotected situations, as on the outer side of a limb, and thinner on the inner side. By Bichat, aponeurotic fasciae were divided into two classes, aperieuroses of insertion, and aponeuroses of investment.

The aponeuroses of insertion serve for the insertion of muscles. Some of these are formed by the expansion of a tendon into an aponeurosis, as, for instance, the tendon of the Sartorius; others do not originate in tendons, as the aponeuroses of the abdominal muscles.

The aponeuroses of investment form a sheath for the entire limb, as well as for each individual muscle. Many aponeuroses, however, serve both for investment and insertion. Thus the deep fascia on the front of the leg gives attachment to the muscles in thia region; and the aponeurosis of insertion given off from the tendon of the Biceps is continuous with the investing fascia of the forearm, and gives origin to the muscles in this region. The deep fasciae assist the muscles in their action, by the degree of tension and pressure they make upon their surface; and in certain situations this is increased and regulated by muscular action, as, for instance, by the Tensor vaginae femoris and Gluteus maximus in the thigh, by the Biceps in the leg, and Palmaris longus in the hand. In the limbs, the fasciae not only invest the entire limb, but give off septa, which separate the various muscles, and are attached beneath to the periosteum; these prolongations of fasciae are usually spoken of as intermuscular septa.

The Muscles and Fasciaa may be arranged, according to the general division of the body, into,
1. Those of the head, face, and neck.
2. Those of the trunk.
3. Those of the upper extremity.
4. Those of the lower extremity.

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