and ears; six are ear bones. With the exception of the lower jaw bone (mandible) and the ear bones, all skull bones are joined together and fixed in one position. The seams where they join are known as sutures.
Cranial Bones.— The cranium is formed by eight cranial bones, six of which are essential to know. The FRONTAL BONE, which forms the forehead, contains the frontal sinuses and helps form the eye socket and nasal cavity. The two PARIETAL BONES form the roof of the skull. The two TEMPORAL BONES, which help form the sides and base of the skull, also house the auditory, or 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.
Facial Bones.— The two MAXILLARY BONES form the upper jaw, nasal walls, and part of the eye socket. These bones contain large cavities called maxillary sinuses. Frequently these sinuses become infected, causing the individual much discomfort. The lower jaw is called the MANDIBLE. Its main function is mastication. Other bones of the face are the LACRIMAL and NASAL BONES.
Figure 3-16.—Vertebral column.
VERTEBRAL (SPINAL) COLUMN.— It consists of 24 movable or true vertebrae, the sacrum, and the coccyx, or tail bone (fig. 3-16). The spinal column is divided into five regions in the following order: cervical (neck), thoracic (chest), lumbar (lower back), and sacral and coccygeal (pelvis).
Figure 3-17.—Vertebra structure.
The vertebrae protect the spinal cord and the nerves arising from the spinal cord. Each vertebra has an anterior portion, the body, which is the large solid segment of the bone (fig. 3-17). This body is for support, not only for the spinal cord, but for other structures of the body as well. Many of the main muscles are attached to the vertebrae. The vertebral foramen is a hole directly behind the body of the vertebrae and forms the passage for the spinal cord. The vertebral projections are for the attachments of muscles and ligaments and 3-8
