SKELETON

term applied to the more or le hard and rigid frame-work of an animal supporting the soft ti ues and protecting the internal organs. In this article the human skeleton is described. Axial Skeleton.—The skull is dealt with elsewhere; see Skuty. The spinal or vertebral column is composed originally of thirty-three vertebre, but in the adult the first twenty-four vertebre remain separate, the next five join together to form the sacrum, and the last four fuse more or le completely to form the coccyx. The vertebra differ in the different regions of the spinal column, but their main characteristics are the same, each po e ing a cylindrical body, which is united by cartilage to the bodies immediately above and below, a neural arch, enclosing the nervous structure termed the spinal cord, formed by two pedicles springing from the body and closed behind by the junction of the Jamina on each side, while from the arch a spinous proce projects backwards, transverse proce es on each side, and above and below on each side articular proce es project, in articulation with similar proce es of the immediately adjacent vertebree. The spinal column is divided into five regions: the cervical, with seven vertebrae; the dorsal, with twelve, with which the ribs articuJate; the lumbar, with five; and the fused sacrum, which forms part of the bony girdle of the pelvis, and coccyz, originally five and four respectively. The ribs are flat, elastic bones, curved in the form of an arch, and compose a protection for the chest. Numbering twelve on each side, the first seven pairs are connected by bars of cartilage with the sternum, while the lower five pairs are more or le free, the first three of them being attached by cartilage to the ribs above but not to the sternum, while the last two are quite free in front, and termed ‘fioating.’ The articulations with the vertebre behind freely allow of the movements of respiration. The sternwm, or breast-bone, is flat and points slightly forwards. limb may be divided into the shoulder, upper arm, fore-arm, and hand. The bones of the shoulder are the clavicle (or collar-bone), which stretches from the scapula to the sternum, with both of which it forms articulations, and is curved, thick, and somewhat triangular at the sternal, and flattened at the scapular end, and the scapula, which is triangular and flat, with a prominent spine projecting right acro its posterior aspect and ending in a broad proce termed the acromion, which articulates with the clavicle, while from the border just above the antero-superior angle juts a curved proce , the coracoid, the articular cup for the humerus, or glenoid fo a, lying below and between the two proce es. The humerus is the bone of the upper arm. The forearm has two bones, the radius on the outer side, and the wan a on the inner side. See diagram. The skeleton of the hand includes the bones of the wrist, carpal bones, eight in number, arranged in two rows—the scaphoid, semilunar, cuneiform, and pistiform above, and the trapezium, trapezoid, os magnum, and unciform below; the bones of the palm, or metacarpal bones, are five in number, with a shaft compre ed in the middle, the extremity nearest the wrist concave, and the farther extremity convex; the bones of the fingers, or phalanges, number three in each finger and two in the thumb, resembling the metacarpal in shape, except that the terminal phalanges have no articular surfaces at their farther extremities. The lower limb may be divided into the haunch, thigh, leg, and foot. The bone of the haunch, or innominate bone, forms part of the bony girdle of the pelvis, the innominate bone of each side joining the sacrum behind and articulating with its fellow of the opposite side at the symphysis pubis in: front. It is an irregular, curved, flat bone, consisting in its earlier stages of development of three bones, the tlium, ischium, and pubis, which only unite completely to form the innominate bone about the twenty-third to twenty-fifth year or life. The three parts join together at the acetabulum (also called the cotyloid cavity), or socket of the hip-joint. The thigh has one bone, the femur, which is a long bone—the longest bone, indeed, of the body. In front of the lower extremity of the femur is a small triangular flat bone, developed in the tendon of the extensor muscles on the front of the thigh, termed the patella (commonly known as the knee-cap), its posterior surface being smooth and forming part of the knee-joint. There are two bones of the leg, the ttbia, and the fibula, which is a thin, slender, long bone with a rigid shaft, a small smooth surface on the upper extremity to articulate with the tibia, and @ proce forming the external malleolus at the lower extremity. The foot includes the tarsal bones, seven in number, arranged in three TOWS, that nearest to the bones of the leg consisting of the astragalus, which has a smooth surface for articulation with the bones of the leg, and the os calcis, the row consisting of the scaphoid, middle and the farthest including cuboid, or external cuneiform, middle cuneiform, and internal cuneiform; the metatarsal bones and phalanges of the toes are the same in number and in their general form as the corresponding metacarpal pones and phalanges in the hand. sae