“It is often stated that there are 206 bones in the skeleton

“It is often stated that there are 206 bones in the skeleton, but this is only a typical adult count, not an invariable number. At birth there are about 270, and even more bones form during childhood. With age, however, the number decreases as separate bones gradually fuse. The fusion of several bones, completed by late adolescence to the mid-20s, brings about the average adult number of 206.” (Saladin, ANATOMY & PHYSIOLOGY, 2015) The skeleton is divided into two regions; the axial skeleton and appendicular skeleton. The axial skeleton (see Table 1) consists of the central supporting axis of the body, including the skull, auditory ossicles, hyoid bone, vertebral column, and thoracic cage (see figure 1 Appendix A). The appendicular skeleton consists of the bones of the upper limb and pectoral girdle and the bones of the lower limb and pelvic girdle (see Table 2). Bones have a variety of ridges, spines, bumps, depressions, canals, pores, slits, cavities, and articular surfaces. Research shows that the skull is the most complex part of the skeleton. It is composed of 22 bones, and sometimes more. “Bones of the skull have especially conspicuous foramina – holes that allow passage for nerves and blood vessels” (Saladin, ANATOMY & PHYSIOLOGY, 2015). Cranial bones are bones that enclose the brain. “The cranium is a rigid structure with an opening, the foramen magnum, where the spinal cord meets the brain” (Saladin, ANATOMY & PHYSIOLOGY, 2015). The vertebral column supports the skull and trunk, allows for their movement, protects the spinal cord, and absorbs stresses produced by walking, running, and lifting. It also provides attachment for the limbs, thoracic cage, and postural muscles. Although normally referred to as the backbone, it consists not of a single bone but a flexible chain of 33 vertebrae with intervertebral discs of fibrocartilage between most of them. There are 12 thoracic vertebrae, corresponding to the 12 pairs of ribs attached to them; no other vertebrae have rib bones. The function of the thoracic vertebrae is to support the thoracic cage enclosing the heart and lungs. Each rib makes a curve around the side of the chest and then progresses anteriorly to approach the sternum. Ribs eight through 12 are false ribs because they lack independent cartilaginous connections to the sternum. The pectoral girdle supports the arm and connects it to the axial skeleton. “It consists of two bones on each side of the body; the clavicle and scapula” (Saladin, ANATOMY & PHYSIOLOGY, 2015). The clavicle is somewhat S-shaped, slightly flattened from the upper to lower surface, and easily seen and palpated on the upper thorax. The scapula, named for its resemblance to a spade or shovel, is a triangular plate that posteriorly overlies rib bones two through seven. “The upper limb is divided into four segments containing a total of thirty bones per limb: the brachium, the antebrachium, the carpus, and the manus… The lower limb is divided into four regions containing a total of thirty bones per limb: the femoral region, the crural, the tarsal region, and the pedal region” (Saladin, ANATOMY & PHYSIOLOGY, 2015). These are adapted for weight bearing and locomotion and are therefore shaped and articulated differently than the upper limb. A large group of joints, tendons, ligaments, and cartilage link the bones of the skeletal system into a functional whole. The skeletal system performs vital functions such as, support movement, protection, blood cell production, calcium storage, and even endocrine regulation. Bones are considered to be living organs because they are made up of nerve, muscle, epithelial tissue, and connective tissue that puts everything together. Within the bones, red and white blood cells are produced, along with platelets. There is a fibrous sheath called a periosteum that contains blood vessels which supply oxygen and nutrients to the bone tissues. Blood vessels get in and out of the bones by tiny openings called nutrient canals. As we develop, our bones grow with us. Hyaline cartilage produces lateral growth, which is further replaced by bone tissue. The skeletal system is covered with muscles that allow us to move. These muscles are attached to the bones through tendons and often stretch from one end to the other. Bones and muscles work together as a team through a series of impulses and signals communicated between brain and skeletal muscles. In order to move, the nervous system signals a skeletal muscle to contract, and when the muscle contracts, this movement causes the attached bone (or bones) to follow.