The skeleton forms the framework of the body, protects vital organs, and works with the muscular system to produce movement. The human adult skeleton is composed of 206 bones. It is divided for study into the axial skeleton and the appendicular skeleton (Fig. 19-1).
The axial skeleton consists of the skull, the spinal column, the ribs, and the sternum. The skull consists of eight cranial bones and the 14 bones of the face (Fig. 19-2). Skull bones are joined by nonmoveable joints (sutures), except for the joint between the lower jaw (mandible) and the temporal bone of the cranium, the temporomandibular joint (TMJ). As shown in Figure 19-3, the 26 vertebrae of the spinal column are divided into five regions: cervical (7); thoracic (12); lumbar (5); the sacrum (5 fused); and the coccyx (4 to 5 fused). Between the vertebrae are disks of cartilage that add strength and flexibility to the spine.
FIGURE 19-1. The skeleton. The axial skeleton is shown in yellow; the appendicular skeleton is shown in blue. (Reprinted with permission from Cohen BJ, Wood DL. Memmler's The Human Body in Health and Disease. 9th Ed. Philadelphia: Lippincott Williams & Wilkins, 2000.)
Coronal Squamous suture suture
□ Parietal □ Maxilla EH Sphenoid EH Zygomatic EH Temporal EH Mandible
FIGURE 19-2. The skull from the left. An additional cranial bone, the ethmoid, is visible mainly from the interior of the skull. (Reprinted with permission from Cohen BJ, Wood DL. Memmler's The Human Body in Health and Disease. 9th Ed. Philadelphia: Lippincott Williams & Wilkins, 2000.)
The appendicular skeleton consists of the bones of the arms and legs, the shoulder girdle, and the pelvis. Each of the two pelvic bones is formed of three fused bones (Fig. 19-4). The large, flared, upper bone is the ilium.
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