Articulations
Synarthrosis, or immoveable
Amphiarthrosis, or mixed
Diarthrosis, or moveable
Kinds of movement
Articulations of the trunk
The vertebral column
The atlas with the axis
The atlas with the occiptal bone
The axis with the occiptal bone
Tempoko-maxillart articulation
The ribs with the vertebras
The cartilages of the ribs with the sternum
Ligaments of the sternum
The pelvis with the spine
The pelvis
Articulations of the upper extremity
Sterno-clavicular articulation
Scapulo-clavicular articulation
Proper ligaments of the scapula
Shoulder joint
Elbow joint
Radio-ulnar articulations
Whist joint
Articulations of the carpus
Capro metacapral articulations
Metacarpo-phalangeal articulations
Articulations of the phalanges
Articulations of the lower extremity
Hip joint
The knee joint
Articulations between the tibia and fibula
Ankle joint
Articulations of the tarsus
Tarso-metatarsal articulations
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The various bones of which the Skeleton consists are connected together at different parts of their surfaces, and such connection is designated by the name of Joint or Articulation. If the joint is immoveable, as between the cranial bones, their adjacent margins are applied in almost close contact, a thin layer of fibrous membrane only being interposed; but in the moveable joints, the bones forming the articulation are generally expanded for greater convenience of mutual connexion, covered by an elastic structure, called cartilage, held together by strong bands, or capsules, of fibrous tissue, called ligament, and lined throughout by a membrane, the synovial membrane, which secretes a fluid which lubricates the various parts of which the joint is formed, so that the structures which enter into the formation of a joint are bone, cartilage, fibro-cartilage, ligament, and synovial membrane.
Bone constitutes the fundamental element of all the joints. In the long bones the extremities are the parts which form the articulations; they are generally somewhat enlarged and expanded, consisting of loose spongy cancellous tissue, with a thin coating of compact substance, which forms their articular surface, and is called the articular lamella. In the flat bones, the articulations usually take place at the edges; and in the short bones, by various parts of their surface. Cartilage is a firm, opaque, blueish-white substance, highly elastic, extremely flexible, and possessed of considerable cohesive power. That form of cartilage which enters into the formation of the joints is called articular cartilage; it forms a thin incrustation upon the articular extremities, or surfaces, of bones, and is admirably adapted, by its elastic property, to break the force of concussions, and afford perfect ease and freedom of movement between the bones. Where it covers the rounded ends of bones, as the extremities of the femur and humerus, it is thick at the centre, and becomes gradually thinner towards the circumference: an opposite arrangement exists where it lines the corresponding cavities. On the articular surfaces of the short bones, as the carpus and tarsus, the cartilage is disposed in a layer of uniform thickness throughout. The attached surface of articular cartilage is closely adapted to the articular lamella; the free surface is smooth, polished, and covered in the foetus by an extremely thin prolongation of synovial membrane, which, however, at a later period of life, cannot be demonstrated. Articular cartilage in the adult does not contain blood-vessels; its nutrition being derived from the vessels of the synovial membrane which skirt the circumference of the cartilage, and from those of the adjacent bone, which are, however, separated from direct contact with the cartilage by means of the articular lamella. Mr. Toynbee has shown, that the minute vessels as they approach the articular lamella dilate, and forming arches, return into the cancellous tissue of the bone. The vessels of the synovial membrane advance forwards with it upon the circumference of the cartilage for a very short distance, and then return in loops; they are only found on the parts not subjected to pressure. In the foetus, and also in certain diseased conditions of the joints, the vessels advance for some distance upon the cartilage. Lymphatic vessels and nerves have not, as yet, been traced in its substance. Fibro-cartilage is also employed in the construction of the joints, contributing to their strength and elasticity. This consists of a mixture of white fibrous and cartilaginous tissues in various proportions; it is to the first of these two constituents that its strength and toughness is chiefly owing and to the latter Its elasticity. The fibro-cartilages admit of arrangement into four groups, inter-articular, inter-osseous, circumferential, and stratiform. The Inter-articular fibro-cartilages (menisci) are flattened fibro-cartilaginous plates, of a round, oval, or sickle-like form, interposed between the articular surfaces of certain joints. They are free on both surfaces, thinner toward their centre than at their circumference, and held in position by their extremities being connected to the surrounding ligaments. The synovial membrane of the joint is prolonged over them a short distance from their attached margin. They are found in the temporo-maxillary, st"rno-clavicular, acromio-clavicular, wrist and knee joints. The Inter-osseous fibre-cartilages are interposed between the bony surfaces of those joints which admit of only slight mobility, as between the bodies of the vertebrae and the symphysis of the pubes; they exist in the form of discs, intimately adherent to the opposed surfaces, being composed of concentric rings of fibrous tissue, with cartilaginous laminae interposed, the former tissue predominating towards the circumference, the latter towards the centre. The Circumferential fibro-cartilages consist of a rim of fibro-cartilage, which surrounds the margins of some of the articular cavities, as the cotyloid cavity of the hip, and the glenoid cavity of the shoulder; they serve to deepen the articular surface and protect the edges of the bone. The Stratiform fibro-cartilages are those which form a thin layer in the osseous grooves, through which the tendons of certain muscles glide. Ligaments are found in nearly all the moveable articulations; they consist of bands of various forms, serving to connect together the articular extremities of bones, and composed mainly of bundles of white fibrous tissue, placed parallel with, or closely interlaced with, one another, and presenting a white, shining, silvery aspect. Ligament is pliant and flexible, so as to allow of the most perfect freedom of movement, but strong, tough, and inextensile, so as not readily to yield under the most severely applied force; it is, consequently, admirably adapted to serve as the connecting medium between the bones. There are some ligaments which consist entirely of yellow elastic tissue, as the ligamenta subflava, which connect together the adjacent arches of the vertebrae. Synovial Membrane is a thin, delicate membrane, which invests the articular extremities of the bones, and is then reflected on the inner surface of the various ligaments which connect the articulating surfaces. It resembles the serous membrane in being a shut sac, but differs in the nature of its secretion, which is thick viscid, and glairy, like the white of egg; and hence termed tynovia. The synovial membranes found in the body admit of subdivision into three kinds, articular, bursal, and vaginal. The Articular Synovial Membranes are found in all the freely moveable (diarthrodial) joints. In the foetus, this membrane may be traced over the entire surface of the cartilages; but in the adult it is wanting, excepting at their circumference, upon which it encroaches for a short distance: it then invests the inner surface of the capsular or other ligaments enclosing the joint, and is reflected over the surface of any tendons passing through its cavity, as the tendon of the Popli-teus in the knee, and the tendon of the Biceps in the shoulder. In some joints, the synovial membrane is thrown into numerous folds, which project forward into the cavity. These folds consist of a reduplication of the synovial membrane, some of them containing fat, and, more rarely, isolated cartilage-cells; the free borders of the longer processes being subdivided into vascular fringe-like processes, the vessels of which have a convoluted arrangement. They are especially distinct in the knee, where they are known as the mucous and alar ligaments, and were described by Clopton Havers as mucilaginous glands, and as the source of the synovial secretion, a view lately revived by Mr. Rainey, who finds them in the bursal and vaginal, as well as in the articular synovial membranes. The Bursal Synovial Membranes (Bursce mucosce) are found interposed between surfaces which move upon each other, producing friction, as in the gliding of a tendon, or of the integument over projecting bony surfaces. They are small shut sacs, connected by areolar tissue with the adjacent parts, and secreting a fluid in their interior analogous to synovia. The bursae admit of a subdivision into two kinds, subcutaneous and deep-seated. The subcutaneous are found in various situations, as between the integument and front of the patella, over the olccranon, the malleoli, and other prominent parts. The deep seated are more numerous, and usually found interposed between muscles or their tendons as they play over projecting bony surfaces, as between the Glutei muscles and surface of the great trochanter. Where one of these exists in the neighbourhood of a joint, it usually communicates with the cavity of the synovial membrane, as is generally the case with the bursa between the tendon of the Psoas and Iliacus, and the capsular ligament of the hip, or the one interposed between the under surface of the Sub-scapularis and the neck of the scapula. The Vaginal Synovial Membranes (synovial sheaths) serve to facilitate the gliding of tendons in the osseo-fibrous canals through which they pass. The membrane is here arranged in the form of a sheath, one layer of which adheres to the wall of the canal, and the other is reflected upon the outer surface of the contained tendon; the space between the two free surfaces of the membrane, being partially filled with synovia. These sheaths are chiefly found surrounding the tendons of the Flexor and Extensor muscles of the fingers and toes, as they pass through the osseo-fibrous canals in the hand or foot. Synovia is a transparent, yellowish-white, or slightly reddish fluid, viscid like the white of egg, having an alkaline reaction, and slightly saline taste. It consists, according to Frerichs, in the ox, of 94*8 5 water, 0*56 mucus and epithelium, 0*07 fat, 3*51 albumen and extractive matter, and 0*99 salts. The Articulations are divided into three classes: Synarthrosis, or immoveable; Amphiarthrosis, or mixed; Diarthrosis, or moveable. |