Axial and Appendicular Skeleton: Bones and Functions
The axial skeleton is the centerpiece of the bony framework. It consists of 69 bones, including the skull, spine, and rib cage. Inside the skull are the cranial bones, facial bones, and small auditory ossicles. Below is the backbone, which is the pillar of bone structure, and consists of the cervical, thoracic, and lumbar vertebrae, besides the sacrum and coccyx. Between the spine and sternum, surrounded by the ribs, is the rib cage, which is an essential part of the axial skeleton, protecting important organs like the heart and lungs.
Skull
The skull is the protector of the brain, eyes, ears, and nose. It consists of 23 bones of the cranium and the skeleton of the face.
The vault is composed of eight bones that fit into fixed joints called sutures:
- Frontal bone: Forms the forehead and contributes to the formation of the nasal orbital (the space where the eyeballs are housed).
- Two temporal bones: Protect the channels that are directed toward the middle and inner ear.
- Occipital bone: Has a hole that connects the skull to the spine.
- Two parietal bones: Form the top and sides of the skull.
- Ethmoid bone: Is located in the midline of the skull.
- Sphenoid bone: Houses the pituitary gland.
Facial Bones
The skeleton of the face is divided into the upper and lower jaw.
- Lower Portion: Consists of the jaw bone, located at the bottom and up the face, setting up the jawbone. Its shape is like a horseshoe.
- Maxilla: Consists of 12 paired bones grouped around the upper jaw, and one unpaired bone (vomer).
Ribs
There are 12 pairs of bones in an arc, whose primary mission is to protect vital organs like the heart and lungs. They are divided into:
- True ribs: The first seven pairs of ribs. Articulated by the sternum.
- False ribs: The last three pairs of ribs, which articulate with the sternum via cartilage.
- Floating Ribs: These are the last two pairs of ribs and are free.
Ribcage
It is a frame comprising 12 thoracic vertebrae in the back, and 12 pairs of ribs that arise from the sides of the thoracic vertebrae, as well as the sternum bone, which is in the front, where the arc of the ribs ends. The true ribs join the sternum by costal cartilages. The short ribs are linked indirectly to the sternum, and the floating ribs are free.
Sternum
It is a flat bone located in the anterior chest. It measures between 15 and 20 cm long and is divided into three parts:
- The manubrium: which is the top, wider part and presents a crevice called the sternal notch.
- The body: which is the central portion and has several grooves that receive the ribs.
- The xiphoid process: the tip of the sternum.
Lower Extremities
The two lower extremities have 62 bones between them and are formed by the pelvic girdle (pelvis), femur or thigh bone, and the bones of the leg and foot.
The pelvis is formed by the pelvic bones, sacrum, and coccyx. The femur (thigh bone) is the longest bone in the human body. The bones of the leg (tibia and fibula) are born at the knee and reach the ankle.
The Foot
It consists of three types of bones: the tarsus, metatarsus, and phalanges.
- Tarsus: Is a group of bones that connect the leg with the metatarsus. These bones are composed of the talus and calcaneus, cuboid bone, navicular, and three cuneiform bones.
- Metatarsals: Extend from the hock to the toes.
- Phalanges: They form the toes. 14 bones are long and are distributed, three for each finger, except the big toe, which has two phalanges.