Review of Key Concepts

Overview of the Skeleton (p. 244)

  1. The skeletal system is divisible into the central axial skeleton (skull, vertebral column, and thoracic cage) and appendicular skeleton (bones of the upper and lower limbs and their supporting girdles).
  2. There are typically 206 named bones in the adult (table 8.1), but the number varies from person to person, it is higher in newborns, and it increases in childhood before bone fusion leads to the adult number of bones.
  3. Before studying individual bones, one must be familiar with the terminology of bone surface features (table 8.2).

The Skull (p. 246)

  1. The skull consists of eight cranial bones, which contact the meninges around the brain, and 14 facial bones, which do not.
  2. It encloses several spaces: the cranial, nasal, buccal, middle-ear, and inner-ear cavities, the orbits, and the paranasal sinuses (frontal, sphenoid, ethmoid, and maxillary).
  3. Bones of the skull are perforated by numerous foramina, which allow passage for cranial nerves and blood vessels.
  4. Some prominent features of the skull in general are the foramen magnum where the spinal cord joins the brainstem; the calvaria, which forms a roof over the cranial cavity; the orbits, which house the eyes; the three cranial fossae that form the floor of the cranial cavity; the hard palate, forming the roof of the mouth; and the zygomatic arches, or "cheekbones."
  5. The cranial bones are the frontal, parietal, temporal, occipital, sphenoid, and ethmoid bones. The parietal and temporal bones are paired, and the others single.
  6. The facial bones are the maxillae; the palatine, zygomatic, lacrimal, and nasal bones; the inferior nasal conchae; and the vomer and mandible. All but the last two are paired. The mandible is the only movable bone of the skull.
  7. Features of the individual bones are summarized in table 8.4.
  8. Associated with the skull are the hyoid bone in the neck and the three auditory ossicles (malleus, incus, and stapes) in each middle ear.
  9. The skull of the fetus and infant is marked by six gaps, or fontanels, where the cranial bones have not fully fused: one anterior, one posterior, two sphenoid, and two mastoid fontanels. A child's skull attains nearly adult size by the age of 8 or 9 years.

The Vertebral Column and Thoracic

Cage (p. 262)

  1. The vertebral column normally consists of 33 vertebrae and 23 cartilaginous intervertebral discs. It is slightly S-shaped, with four curvatures: cervical, thoracic, lumbar, and pelvic.
  2. A typical vertebra exhibits a body, a vertebral foramen, a spinous process, and two transverse processes. The shapes and proportions of these features, and some additional features, distinguish vertebrae from different regions of the vertebral column (table 8.6).
  3. There are five classes of vertebrae, numbering 7 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 4 coccygeal vertebrae in most people. In adults, the sacral vertebrae are fused into a single sacrum and the coccygeal vertebrae into a single coccyx.
  4. An intervertebral disc is composed of a gelatinous nucleus pulposus enclosed in a fibrous ring, the annulus fibrosus.
  5. The thoracic cage consists of the thoracic vertebrae, the sternum, and the ribs.
  6. The sternum has three parts: manubrium, body, and xiphoid process.
  7. There are 12 pairs of ribs. Ribs 1 through 7 are called true ribs because each has its own costal cartilage connecting it to the sternum; 8 through 12 are called false ribs, and 11 and 12, the only ones with no costal cartilages, are also called floating ribs.

The Pectoral Girdle and Upper

Limb (p. 270)

  1. The pectoral girdle attaches the upper limb to the axial skeleton. It consists of a scapula (shoulder blade) and clavicle (collar bone) on each side. The clavicle articulates with the sternum and the scapula articulates with the humerus.
  2. The upper limb bones are the humerus in the brachium; the lateral radius and medial ulna in the antebrachium (forearm); eight carpal bones in the wrist; five metacarpal bones in the hand; two phalanges in the thumb; and three phalanges in each of the other four digits.

The Pelvic Girdle and Lower

Limb (p. 277)

  1. The pelvic girdle attaches the lower limb to the axial skeleton. It consists of the sacrum, coccyx, and two ossa coxae. Each adult os coxae results from the fusion of three bones of the child: the ilium, ischium, and pubis.
  2. The pelvic girdle forms two basinlike structures: a superior, wide false (greater) pelvis and an inferior, narrower true (lesser) pelvis. The passage from the false to the true pelvis is called the pelvic inlet and its margin is the pelvic brim; the exit from the true pelvis is called the pelvic outlet.
  3. Two other major features of the os coxa are the iliac crest, which forms the flare of the hip, and the acetabulum, the cuplike socket for the femur.
  4. The lower limb bones are the femur in the thigh; the lateral fibula and larger, medial tibia in the leg proper; seven tarsal (ankle) bones forming the posterior half of the foot; five metatarsal bones in its anterior half; two phalanges in the great toe; and three phalanges in each of the other digits.

Saladin: Anatomy & I 8. The Skeletal System I Text I © The McGraw-Hill

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