Axial Bones

Bones protect soft body parts and make movement possible; they also

serve as landmarks for locating parts of other body systems.

2. The musculoskeletal system is composed of the bones, joints, and muscles

working together.

7.1 Divisions of the Skeletal System (see Table 7.1)

1. The axial skeleton consists of bones arranged along the longitudinal axis.

The parts of the axial skeleton are the skull, auditory ossicles (ear bones), hyoid

bone, vertebral column, sternum, and ribs.

2. The appendicular skeleton consists of the bones of the girdles and the upper

and lower limbs (extremities). The parts of the appendicular skeleton are the

pectoral (shoulder) girdles, bones of the upper limbs, pelvic (hip) girdles, and

bones of the lower limbs.

7.2 Types of Bones

1. On the basis of shape, bones are classified as long, short, flat, irregular, or

sesamoid. Sesamoid bones develop in tendons or ligaments.

2. Sutural bones are found within the sutures of some cranial bones.

7.3 Bone Surface Markings

1. Surface markings are structural features visible on the surfaces of bones.

2. Each marking—whether a depression, an opening, or a process—is

structured for a specific function, such as joint formation, muscle attachment,

or passage of nerves and blood vessels (see Table 7.2).

7.4 Skull: An Overview

1. The 22 bones of the skull include cranial bones and facial bones.

2. The eight cranial bones are the frontal, parietal (2), temporal (2), occipital,

sphenoid, and ethmoid.

3. The 14 facial bones are the nasal (2), maxillae (2), zygomatic (2), lacrimal (2),

palatine (2), inferior nasal conchae (2), vomer, and mandible.

7.5 Cranial Bones

1. The frontal bone forms the forehead (the anterior part of the cranium).

2. The frontal bone also forms the roofs of the orbits and most of the anterior

part of the cranial floor.

3. The parietal bones form the greater portion of the sides of the cranial cavity.

4. The parietal bones also form most of the roof of the cranial cavity.

5. The temporal bones form the inferior lateral aspects of the cranium.

6. The temporal bones also form part of the cranial floor.

7. The occipital bone forms the posterior part of the cranium.

8. The occipital bone also forms of the base of the cranium.

9. The sphenoid bone lies at the middle part of the base of the skull.

10. The sphenoid bone is known as the keystone of the cranial floor because it

articulates with all the other cranial bones, holding them together.

11. The ethmoid bone is located in the anterior part of the cranial floor medial

to the orbits.

Chapter Review 231

12. The ethmoid bone is anterior to the sphenoid and posterior to the nasal

bones.

7.6 Facial Bones

1. The nasal bones from the bridge of the nose.

2. The lacrimal bones are posterior and lateral to the nasal bones and form a

part of the medial wall of each orbit.

3. The palatine bones form the posterior portion of hard palate, part of the floor

and lateral wall of the nasal cavity, and a small portion of the floors of the orbits.

4. The inferior nasal conchae form a part of the inferior lateral wall of the nasal

cavity and project into the nasal cavity.

5. The vomer forms the inferior portion of the nasal septum.

6. The maxillae form the upper jawbone.

7. The zygomatic bones (cheekbones) form the prominences of the cheeks

and part of the lateral wall and floor of each orbit.

8. The mandible is the lower jawbone, the largest and strongest facial bone.

7.7 Special Features of the Skull

1. The nasal septum consists of the vomer, perpendicular plate of the ethmoid,

and septal cartilage. The nasal septum divides the nasal cavity into left and

right sides.

2. Seven skull bones form each of the orbits (eye sockets).

3. The foramina of the skull bones provide passages for nerves and blood vessels.

4. Sutures are immovable joints that connect most bones of the skull.

Examples are the coronal, sagittal, lambdoid, and squamous sutures.

5. Paranasal sinuses are cavities in bones of the skull that are connected to

the nasal cavity. The frontal, sphenoid, and ethmoid bones and the maxillae

contain paranasal sinuses.

6. Fontanels are mesenchyme-filled spaces between the cranial bones

of fetuses and infants. The major fontanels are the anterior, posterior,

anterolaterals (2), and posterolaterals (2). Aft er birth, the fontanels fill in with

bone and become sutures.

7.8 Hyoid Bone

1. The hyoid bone is a U-shaped bone that does not articulate with any other

bone.

2. It supports the tongue and provides attachment for some tongue muscles

and for some muscles of the pharynx and neck.

7.9 Vertebral Column

1. The vertebral column, sternum, and ribs constitute the skeleton of the

body’s trunk.

2. The 26 bones of the adult vertebral column are the cervical vertebrae (7),

the thoracic vertebrae (12), the lumbar vertebrae (5), the sacrum (5 fused

vertebrae), and the coccyx (usually 4 fused vertebrae).

3. The adult vertebral column contains four normal curves (cervical, thoracic,

lumbar, and sacral) that provide strength, support, and balance.

4. Each vertebra usually consists of a body, vertebral arch, and seven

processes. Vertebrae in the diff erent regions of the column vary in size, shape,

and detai