CHAPTER XVI.

Bones-Their number-uses-arrangement-composition-growth

diseases-Fractures-varieties-symptoms-Special fractures— The process of repair-The treatment of fractures-Splints, etc.Plaster-of-Paris bandages-Starch-Water-glass-Fracture-boxExtensions-Handling fractured limbs-Dislocations-How distinguished from fractures-How reduced-Sprains-Anchylosis.

THE human skeleton is composed of more than two hundred different bones. These bones constitute the framework of the body, and serve to protect the delicate vital organs. There are three important cavities in the body, the skull, the chest, and the pelvis, each wholly or partly inclosed by bone, and held in position by the spinal column. This itself forms a canal containing the spinal cord, a continuation of the substance of the brain.

The skull is divided into two parts: the cranium, composed of eight, and the face of fourteen bones, besides those of the ears. The seams, or lines of union, of these bones are called sutures; that between the two parietal bones is the sagittal suture, that connecting the parietals with the frontal is the coronal suture, that between the occipital and the parietals, the lambdoidal. These are the most important ones.

The head rests upon the first of the spinal vertebræ, which is called the atlas. The one next to this is the axis; these two allow the movements of the head in every direction. The spine consists of thirty-three

bones, called cervical, dorsal and lumbar vertebræ, according to the position which they occupy. Those of the different groups have differences also in shape by which they are recognizable.

From either side of the dorsal vertebræ spring twelve ribs, forming the framework of the thorax or chest. The first seven are connected in front with the sternum or breast bone, and are called true ribs; the lower five are distinguished as false ribs, three of them being connected only with the costal cartilages in front, and the last two having no attachment except to the vertebræ. These are termed floating ribs. At the lower extremity of the sternum is the ensiform cartilage. Joined to the upper end of the sternum in front, and to the scapula, or shoulder blade, in the back, is the clavicle or collar-bone; also, fitting into a cavity of the scapula, is the humerus, the largest bone of the arm. The upper arm has but this one bone; the forearm has two, the ulna and the radius. The ulna is the larger. It makes a perfect hinge-joint with the humerus. The two prominences at the elbow are called respectively the olecranon and the coronoid processes. The lower end of the ulna articulates with the radius but does not enter into the wrist-joint. This is formed by the lower and larger extremity of the radius, articulating with the eight small bones which make the carpus or wrist. Besides these there are in the hand five metacarpal bones, forming the palm, and fourteen phalanges, three in each finger, and two in the thumb.

The back of the pelvic wall is formed by the sacrum. This consists, in early life, of five distinct bones, which later become fused into one. The coccyx, the extreme end of the spinal column, is also formed by the union of four small bones. The remaining walls of the pelvic

cavity are composed, on each side, of three bones, the ilium, ischium, and pubes, uniting in adult life into one, the os innominatum.

The lower extremity of the body has its bones arranged very much like those of the arm. The thigh bone or femur is the largest bone in the body. It has a round head, which fits into a cup-like cavity of the os innominatum, called the acetabulum; below this is a narrow neck, and two bony projections, the greater and less trochanters. The lower end of the femur articulates with the tibia, the larger bone of the leg. In front of the knee-joint is a thick triangular bone, the patella or knee-pan. Parallel with the tibia is a much smaller bone, the fibula. The foot has three divisions-the tarsus, having seven bones, the metatarsus, of five, and fourteen phalanges, arranged like those of the hand.

The skull contains the brain and organs of special sense; the thorax the organs of circulation and respiration, while the lower part of the trunk sustains those of digestion and reproduction.

The bones are composed of about two parts of mineral to one of animal matter. Lime is the main mineral, and gelatine the predominant animal constituent. Each bone is enveloped in a white fibrous membrane, known as the periosteum. This supplies nutrition to the bone. At the joints, or articulations, the bones are covered with a layer of smooth, somewhat elastic cartilage, and furnished with a serous membrane which secretes a lubricating fluid, the synovia. Bones increase in length by the ossification of these layers of cartilage-a new layer being deposited as the older one hardens into bone; this growth is more rapid at the lower ends of the bones. Similarly they increase in thickness, by the continual conversion of the periosteum into osseous