SKULL.—The skull consists of 28 bones (figs. 1-15 and 1-16), 22 of which form the framework of the head and provide protection for the brain, eyes, and ears; six are ear bones. With the exception of the lower jaw bone and the ear bones, all skull bones are joined together and fixed in one position. The seams where they join are known as sutures. The bones of the skull are classified as either cranial or facial bones. Cranial Bones.—The cranium is formed by eight major bones, most of which are in pairs (fig. 1-15). The frontal bone forms the forehead and the roof of each orbit (or eye socket) and the nasal cavity. The parietal bones form the roof of the skull. The temporal bones help form the sides and base of the skull and also house the auditory and hearing organs. The occipital bone forms part of the base and back of the skull, and contains a large hole called the foramen magnum. This opening permits passage of the spinal cord from the cranium into the spinal column. The sphenoid bones are wedged between several other bones in the anterior portion of the skull. These bones help form the base of the cranium, the sides of the skull, and the floors and sides of the orbits. The ethmoid bones are located in front of the sphenoid bone. They form sections of the nasal cavity roof, the cranial floor, and the orbital wall. Facial Bones.—The facial bones of the skull consists of 14 bones: 13 immovable bones and a movable lower jawbone (fig. 1-16). The facial bones give the face its basic shape and provide attachment sites for various muscles that move the jaw and control facial expressions. 1-8 HM3F0114 EPIPHYSEAL DISKS PROXIMAL EPIPHYSIS ARTICULAR CARTILAGE SPACE OCCUPIED BY RED MARROW CANCELLOUS TISSUE COMPACT BONE MEDULLARY CANAL YELLOW MARROW PERIOSTEUM DIAPHYSIS DISTAL EPIPHYSIS SPONGY BONE Figure 1-14.—Anatomy of a long bone. HM3f0115 MENTAL FORAMEN MANDIBLE CORONAL SUTURE FRONTAL BONE SPHENOID BONE ETHMOID BONE LACRIMAL BONE NASAL BONE ZYGOMATIC BONE INFRAORBITAL FORAMEN ZYGOMATIC PROCESS OF TEMPORAL TEMPORAL PROCESS OF ZYGOMATIC OCCIPITAL BONE TEMPORAL BONE LAMBDOIDAL SUTURE SQUAMOSAL SUTURE PARIETAL BONE MAXILLA Figure 1-15.—Lateral view of the skull.