Chapter 5 The Skeletal System 125 Copyright Goodheart-Willcox Co., Inc. The thoracic region encompasses the next 12 vertebrae, which extend through the chest region and articulate (connect) with the ribs. The thoracic vertebrae are larger than those in the cervical region. They have large, thick bodies and prominent spinous and transverse processes. Costal facets on these vertebrae articulate with the heads of the ribs. The lumbar region includes the five vertebrae found in the lower back. These are the largest of the vertebrae with the thickest bodies. Lumbar vertebrae are well designed for supporting all the weight of the trunk, head, and arms. The sacrum consists of five fused vertebrae that form the posterior portion of the pelvic girdle, artic- ulating with the L5 vertebrae above and the coccyx SELF CHECK 1. Scientists often divide the human skeleton into two parts. What are these parts called? 2. Which bones make up the axial skeleton? 3. What holds the bones of the skull together? Is movement possible at these joints? Why is this important? 4. List the two functions of the fontanels in a baby’s skull. 5. List the eight cranial bones and tell where each is found. 6. List the fourteen facial bones and tell where each is found. Vertebral Column Although the word spine suggests a straight, rigid bar, the human spine, or vertebral column, is anything but straight and rigid. The human spinal column is well designed to perform its functions of protecting the extremely delicate spinal cord, while supporting the weight of the trunk and allowing flexibility in multiple directions. Thirty-three stacked, individual bones called vertebrae comprise the spine. The vertebrae differ in size and shape in the different regions of the spine to best fulfill their respective functions (Figure 5.13). Regions of the Spine There are five named sections of the spine. These include the cervical, thoracic, and lumbar regions, as well as the sacrum, and coccyx. The cervical region (neck) includes the upper seven vertebrae that enable the head to nod up and down and rotate to the right and left. The first cervical vertebra, the atlas, is specialized to provide the connection between the occipital bone of the skull and the spinal column (Figure 5.14). (The atlas is so-called after the mythical Greek Titan named Atlas, who was condemned to hold up the weight of the world for an eternity.) The second cervical vertebra, the axis, is also specialized, with an upward projection called the odontoid process or dens, on which the atlas rotates. The cervical vertebrae are the smallest of the vertebrae, and they are characterized by relatively short spinous processes. They include large vertebral foramina, as well as foramina that serve as passageways for the vertebral arteries connecting upward to the brain region. Cervical region C5 C6 C7 T1 T2 T3 T5 T4 L1 L2 L3 L5 L4 T6 T7 T8 T9 T10 T11 T12 C1 C2 C3 C4 Thoracic region Lumbar region Sacrum Cervical curve Thoracic curve Lumbar curve Sacral curve Coccyx © Body Scientifi c International Figure 5.13 The vertebral column (spine).