to facilitate movement of one vertebra over the fusion of five false vertebrae. It articulates on another.
There are seven cervical vertebrae in the neck. The first is called the ATLAS and resembles a bony ring. It supports the head. The second is the highly specialized AXIS. It has a bony prominence that fits into the ring of the atlas, thus permitting the head to rotate from side to side. The atlas and the axis are the only named vertebrae, all others are numbered. Each cervical vertebrae has a transverse foramen to allow passage of nerves, the vertebral artery, and a vein. The seventh cervical vertebra has an especially prominent projection that can easily be felt at the nape of the neck. This makes it possible for physicians to count and identify the vertebrae above and below it.
There are 12 vertebrae in the thoracic region. These articulate with the posterior portion of the 12 ribs to form the posterior wall of the thoracic, or chest, cage.
There are five lumbar vertebrae, which are the largest segments of the vertebral column.
The SACRUM is the triangular bone immediately below the lumbar vertebrae, formed by each side with the hip bone and with the COCCYX to form the posterior wall of the PELVIS.
THORAX.— It is a cone-shaped bony cage, about as wide as it is deep (fig. 3-18). It is formed by 12 ribs on each side, which articulate posteriorly with the thoracic vertebrae. The first seven pairs of ribs are attached to the sternum by cartilage and are called true ribs. The eighth, ninth, and tenth ribs are united by their cartilages to the cartilage of the seventh rib and are called false ribs. The STERNUM is an elongated flat bone, forming the middle portion of the upper half of the chest wall in front. The xiphoid process, located at the inferior aspect of the sternum, serves as a landmark in the administration of cardiopulmonary resuscitation.
Figure 3-18.—Thorax, anterior view.
Appendicular Skeleton
UPPER EXTREMITY.— The upper extremity consists of the bones of the shoulder, the arm,