Chapter 4 The Skeletal System 135 Check Your Understanding 1. Scientists often divide the human skeleton into two parts. What are these parts called? 2. What holds the bones of the skull together? Is movement possible at these joints? Why is this important? 3. List the two functions of the fontanels in a baby’s skull. 4. List the eight cranial bones and tell where each is found. 5. List the fourteen facial bones and tell where each is found. The 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 vertebral 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 (VER-teh-bray) comprise the spine. The vertebrae differ in size and shape in the different regions of the spine to best fulfill their respective functions (Figure 4.11). Regions of the Spine There are five named sections of the spine: 1. The cervical (SER-vi-kal) region (neck) includes the upper seven vertebrae that enable nodding the head up and down, as well as rotation 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 4.12). The second cervical vertebra, the axis, is also specialized, with an upward projection called the odontoid process, on which the atlas rotates. 2. The thoracic (thoh-RAS-ik) region encompasses the next 12 vertebrae, which extend through the chest region and articulate (connect) with the ribs. • the frontal bone, which forms the forehead • the two paired parietal (pah-RIGH-eh-tal) bones, which form the majority of the top and sides of the skull • the two paired temporal (TEHM-poh-ral) bones, which surround the ears • the occipital (ahk-SIP-i-tal) bone, which forms the base and lower back portions of the skull • the ethmoid (EHTH-moyd) bone, which forms part of the nasal septum • the sphenoid (SFEE-noyd) bone, which is butterfly shaped and centrally located within the skull. The sphenoid bone supports part of the base of the brain, forms part of the orbits of the eyes, and is connected to all of the other bones of the skull. The Facial Bones A total of fourteen bones form the face, including the mandible (MAN-di-buhl), vomer (VOH-mer), and six pairs (left and right) of bones. The facial bones include: • the two fused maxillary (MAK-si-lair-ee) bones, which form the upper jaw, house the upper teeth, and connect to all other bones of the face, with the exception of the mandible • the two palatine (PAL-a-tighn) bones, which form the posterior part of the hard palate, or roof of the mouth • the two zygomatic (zigh-goh-MAT-ik) bones, or cheekbones, which also form much of the sides of the orbits, or eye sockets • the two lacrimal (LAK-ri-mal) bones, tiny bones connecting to the orbits and surrounding the tear ducts • the two nasal bones, forming the bridge of the nose • the vomer (plow-shaped) bone, comprising most of the bony nasal septum • the two inferior concha (KAHN-ka) bones, forming the sides of the nasal cavity • the mandible, or lower jawbone, which is the largest facial bone, as well as the only movable facial bone. Copyright Goodheart-Willcox Co., Inc.