THE GENERAL framework of the body is built up mainly of a series of bones, supplemented, however, in certain regions by pieces of cartilage; the bony part of the framework constitutes the skeleton.Bones are divisible into four classes: Long, Short, Flat, and Irregular.

Long Bones are consists of a body or shaft and two extremities. The body, or diaphysis is cylindrical, with a central cavity termed the medullary canal that filled with marrow.The extremities (epiphyses) are generally expanded, for the purposes of articulation and to afford broad surfaces for muscular attachment.

The long bones are not straight, but curved, the curve generally taking place in two planes, thus affording greater strength to the bone. The bones belonging to this class are: the clavicle, humerus, radius, ulna, femur, tibia, fibula, metacarpals, metatarsals, and phalanges.

Where a part of the skeleton is intended for strength and compactness combined with limited movement, it is constructed of a number of short bones, as in the carpus and tarsus.

Where the principal requirement is either extensive protection or the provision of broad surfaces for muscular attachment, the bones are expanded into broad, flat plates, as in the skull and the scapula. These bones are composed of two thin layers of compact tissue enclosing between them.

The intervening cancellous tissue is called the diplo, and this, in certain regions of the skull, becomes absorbed so as to leave spaces filled with air (air-sinuses) between the two tables. The flat bones are: the occipital, parietal, frontal, nasal, lacrimal, vomer, scapula, os cox (hip bone), sternum, ribs, and, according to some, the patella.

SCAPULA BONEFRONTAL BONE

The irregular bones are such as, from their peculiar form, cannot be grouped under the preceding heads. They consist of cancellous tissue enclosed within a thin layer of compact bone. The irregular bones are: the vertebr, sacrum, coccyx, temporal, sphenoid, ethmoid, zygomatic, maxilla, mandible, palatine, inferior nasal concha, and hyoid.

VERTEBRAL BONEMAXILLA BONE

If the surface of a bone be examined, certain eminences and depressions are seen. These eminences and depressions are of two kinds: articular and non-articular. Well-marked examples of articular eminences are found in the heads of the humerus and femur; and of articular depressions in the glenoid cavity of the scapula, and the acetabulum of the hip bone.

Non-articular eminences are designated according to their form. Thus, a broad, rough, uneven elevation is called a tuberosity, protuberance, or process, a small, rough prominence, a tubercle; a sharp, slender pointed eminence, a spine; a narrow, rough elevation, running some way along the surface, a ridge, crest, or line.

Non-articular depressions are also of variable form, and are described as foss, pits, depressions, grooves, furrows, fissures, notches, etc. These non-articular eminences and depressions serve to increase the extent of surface for the attachment of ligaments and muscles.A short perforation is called a foramen, a longer passage a canal.

Bone is one of the hardest structures of the animal body; it possesses also a certain degree of toughness and elasticity. Its color, in a fresh state, is pinkish-white externally, and deep red within.

Bone during life is permeated by vessels, and is enclosed in a fibrous membrane, the periosteum, except where it is coated with articular cartilage.The bloodvessels of bone are very numerous. Those of the compact tissue are derived from a close and dense network of vessels ramifying in the periosteum. From this membrane vessels pass into the minute orifices in the compact tissue, and run through the canals which traverse its substance.

A joint is the location at which two or more bones make contact.They are constructed to allow movement and provide mechanical support, and are classified structurally and functionally.

Structural classification is determined by how the bones connect to each other,while functional classification is determined by the degree of movement between the articulating bones.

There are three structural classifications of joints:fibrous joint - joined by fibrous connective tissuecartilaginous joint - joined by cartilagesynovial joint - not directly joined

The fibrous joints are further divided into three types:Sutures are found between bones of the skull. In fetal skulls the sutures are wide to allow slight movement during birth. They later become rigid (synarthrodial).Syndesmosis are found between long bones of the body, such as the radius and ulna in forearm and the fibula and tibia in leg. Unlike other fibrous joints, syndesmoses are moveable (amphiarthrodial), although not to such degree as synovial joints.Gomphosis is a joint between the root of a tooth and the sockets in the maxilla or mandible.

Joints can also be classified functionally, by the degree of mobility they allow:synarthrosis - permits little or no mobility. Most synarthrosis joints are fibrous joints.amphiarthrosis - permits slight mobility. Most amphiarthrosis joints are cartilaginous joints.diarthrosis - permits a variety of movements. All diarthrosis joints are synovial joints.

A synarthrosis is a type of joint which permits little or no mobility. Most synarthrosis joints are fibrous.Suture joints and synchondroses are synarthrose.They can be categorised by how the two bones are joined together:Synchondroses are joints where the two bones are connected by a piece of cartilage.Synostoses are where two bones that are initially separted eventually fuse together, essentially becoming one bone. In humans the plates of the cranium fuse together as a child approaches adulthood. Children whose craniums fuse too early may suffer deformities and brain damage as the skull does not expand properly to accommodate the growing brain, a condition known as craniostenosis.

Cartilaginous joints are connected entirely by cartilage (fibrocartilage or hyaline).Cartilaginous joints allow more movement between bones than a fibrous joint but less than the highly mobile synovial joint. An example would be the joint between the manubrium and the sternum. Cartilaginous joints also forms the growth regions of immature long bones and the intervertebral discs of the spinal column.

In amphiarthroses, the contiguous bony surfaces are either:symphysis: connected by broad flattened disks of fibrocartilage, of a more or less complex structure, as in the articulations between the bodies of the vertebrae. An example is the sternocostal joint.syndesmosis: united by an interosseous ligament, as in the inferior tibiofibular articulation.

NameExampleDescriptionGliding joints (or planar joints)the carpals of the wristThese joints allow a wide variety of movement, but not much distance.Hinge jointsthe elbow (between the humerus and the ulna)These joints act like a door hinge, allowing flexion and extension in just one plane.Pivot jointsthe elbow (between the radius and the ulna)This is where one bone rotates about another.Condyloid joints (or ellipsoidal joints)the wristA condyloid joint is where two bones fit together with an odd shape (e.g. an ellipse), and one bone is concave, the other convex. Some classifications make a distinction between condyloid and ellipsoid joints.Saddle jointsthe thumb (between the metacarpal and carpal)Saddle joints, which resemble a saddle, permit the same movements as the condyloid joints.Ball and socket jointsthe shoulder and hip jointsThese allow a wide range of movement

Where slight movement combined with great strength is required, the osseous surfaces are united by tough and elastic fibrocartilages, as in the joints between the vertebral bodies, and in the interpubic articulation.In the freely movable joints the surfaces are completely separated; the bones forming the articulation are expanded for greater convenience of mutual connection, covered by cartilage and enveloped by capsules of fibrous tissue.

The cells lining the interior of the fibrous capsule form an imperfect membranethe synovial membranewhich secretes a lubricating fluid. The joints are strengthened by strong fibrous bands called ligaments, which extend between the bones forming the joint.