Major bones of the skeleton. {a) Anterior view. {b) Posterior view. The axial portions are shown in red, and the appendicular portions are shown in brown.

2. Upper limbs. Each upper limb consists of a humerus (hu'mer-us), or arm bone; two forearm bones—a radius (ra'de-us) and an ulna (ul'nah); and a hand. The humerus, radius, and ulna articulate with each other at the elbow joint. At the distal end of the radius and ulna is the hand. There are eight carpals (kar'palz), or wrist bones. The five bones of the palm are called metacarpals (met"ah-kar'palz), and the fourteen finger bones are called phalanges (fah-lan'jez).

3. Pelvic girdle. The pelvic girdle is formed by two os coxae (ahs kok'se), or hipbones, which are attached to each other anteriorly and to the sacrum posteriorly. They connect the bones of the lower limbs to the axial skeleton and, with the sacrum and coccyx, form the pelvis, which protects the lower abdominal and internal reproductive organs.

4. Lower limbs. Each lower limb consists of a femur (fe'mur), or thigh bone; two leg bones—a large tibia (tib'e-ah), or shin bone, and a slender fibula (fib'u-lah), or calf bone; and a foot. The femur and tibia articulate with each other at the knee joint, where the patella (pah-tel'ah), or kneecap, covers the

Muscles Moving The Hyoid Bone

Hyoid bone


Figure 7.18

The hyoid bone supports the tongue and serves as an attachment for muscles that move the tongue and function in swallowing.

Hyoid bone


Figure 7.18

The hyoid bone supports the tongue and serves as an attachment for muscles that move the tongue and function in swallowing.

anterior surface. At the distal ends of the tibia and fibula is the foot. The foot includes the ankle, instep, and toes. There are seven tarsals (tahr'salz). The five bones of the instep are called metatarsals (met"ah-tar'salz), and the fourteen bones of the toes (like the fingers) are called phalanges. Table 7.4 defines some terms used to describe skeletal structures.

Distinguish between the axial and appendicular skeletons.

List the bones of the axial skeleton and of the appendicular skeleton.


A human skull usually consists of twenty-two bones that, except for the lower jaw, are firmly interlocked along lines called sutures. Eight of these interlocked bones make up the cranium, and thirteen form the facial skeleton. The mandible (man'di-b'l), or lower jawbone, is a movable bone held to the cranium by ligaments (figs. 7.19 and 7.21). Some facial and cranial bones together form the orbit of the eye (fig. 7.20). Plates 8-36 on pages 255-269 show a set of photographs of the human skull and its parts.


The cranium (kra'ne-um) encloses and protects the brain, and its surface provides attachments for muscles that make chewing and head movements possible. Some of the cranial bones contain air-filled cavities called sinuses, which are lined with mucous membranes and connect by passageways to the nasal cavity. Sinuses reduce the weight of the skull and increase the intensity of the voice by serving as resonant sound chambers.

The eight bones of the cranium (table 7.5) are as follows:

1. Frontal bone. The frontal (frun'tal) bone forms the anterior portion of the skull above the eyes, including the forehead, the roof of the nasal cavity, and the roofs of the orbits (bony sockets) of the eyes. On the upper margin of each orbit, the frontal bone is marked by a supraorbital foramen through which blood vessels and nerves pass to the tissues of the forehead. Within the frontal bone are two frontal sinuses, one above each eye near the midline. The frontal bone is a single bone in adults, but it develops in two parts (see fig. 7.33). These halves grow together and usually completely fuse by the fifth or sixth year of life.

2. Parietal bones. One parietal (pah-ri'e-tal) bone is located on each side of the skull just behind the frontal bone. Each is shaped like a curved plate and has four borders. Together, the parietal bones form the bulging sides and roof of the cranium. They are fused at the midline along the sagittal suture, and they meet the frontal bone along the coronal suture.

3. Occipital bone. The occipital (ok-sip'i-tal) bone joins the parietal bones along the lambdoidal (lam'doid-al) suture. It forms the back of the skull




condyle (kon'dTl)

A rounded process that usually articulates with another bone

Occipital condyle of the occipital bone (fig. 7.22)

crest (krest)

A narrow, ridgelike projection

Iliac crest of the ilium (fig. 7.50)

epicondyle (ep"T-kon'dTl)

A projection situated above a condyle

Medial epicondyle of the humerus (fig. 7.45)

facet (fas'et)

A small, nearly flat surface

Facet of a thoracic vertebra (fig. 7.38)

fissure (fish' Or)

A cleft or groove

Inferior orbital fissure in the orbit of the eye (fig. 7.20)

fontanel (fon"tah-nel')

A soft spot in the skull where membranes cover the space between bones

Anterior fontanel between the frontal and parietal bones (fig. 7.33)

foramen (fo-ra'men)

An opening through a bone that usually serves as a passageway for blood vessels, nerves, or ligaments

Foramen magnum of the occipital bone (fig. 7.22)

fossa (fos'ah)

A relatively deep pit or depression

Olecranon fossa of the humerus (fig. 7.45)

fovea (fo've-ah)

A tiny pit or depression

Fovea capitis of the femur (fig. 7.53)

head (hed)

An enlargement on the end of a bone

Head of the humerus (fig. 7.45)

linea (lin'e-ah)

A narrow ridge

Linea aspera of the femur (fig. 7.53)

meatus (me-a'tus)

A tubelike passageway within a bone

External auditory meatus of the ear (fig. 7.21)

process (pros'es)

A prominent projection on a bone

Mastoid process of the temporal bone (fig. 7.21)

ramus (ra'mus)

A branch or similar extension

Ramus of the mandible (fig. 7.31)

sinus (si'nus)

A cavity within a bone

Frontal sinus of the frontal bone (fig. 7.27)

spine (spTn)

A thornlike projection

Spine of the scapula (fig. 7.43)

suture (soo'cher)

An interlocking line of union between bones

Lambdoidal suture between the occipital and parietal bones (fig. 7.21)

trochanter (tro-kan'ter)

A relatively large process

Greater trochanter of the femur (fig. 7.53)

tubercle (tu'ber-kl)

A small, knoblike process

Tubercle of a rib (fig. 7.41)

tuberosity (tu"be-ros' 1-te)

A knoblike process usually larger than a tubercle

Radial tuberosity of the radius (fig. 7.46)

Parietal bone

Frontal bone Coronal suture Lacrimal bone Ethmoid bone

Squamosal suture Sphenoid bone Temporal bone

Perpendicular plate of the ethmoid bone

Infraorbital foramen Vomer bone


Lacrimal Canal From Anterior View

Supraorbital foramen

Nasal bone Sphenoid bone Middle nasal concha Zygomatic bone Inferior nasal concha


Mental foramen

Figure 7.19

Anterior view of the skull.

Supraorbital notch

Squamosal Sinus Canals

Figure 7.20

The orbit of the eye includes both cranial and facial bones.

Optic canal Nasal bone

Ethmoid bone Lacrimal bone Maxilla-

Optic canal Nasal bone

Ethmoid bone Lacrimal bone Maxilla-

Infraorbital foramen

Figure 7.20

The orbit of the eye includes both cranial and facial bones.

Superior orbital fissure

Sphenoid bone

Palatine bone

Inferior orbital fissure

■ Zygomatic bone

Parietal bone ■

Squamosal suture Temporal bone Lambdoidal suture

Occipital bone

Temporal process of zygomatic

External auditory meatus

Mastoid process Styloid process

Mandibular condyle

Zygomatic process of temporal

Coronoid process

Figure 7.21

Lateral view of the skull.

Mastoid process Styloid process

Mandibular condyle

Zygomatic process of temporal

Zygomatic Process Frontal Skull Label

- Coronal suture

Frontal bone Sphenoid bone

Ethmoid bone Lacrimal bone

Nasal bone

Zygomatic bone Infraorbital foramen Maxilla

Mental foramen Mandible

Figure 7.22

Inferior view of the skull.

Skull Bones Superior View

Figure 7.22

Inferior view of the skull.

Name and Number


Special Features

Frontal (1)

Forms forehead, roof of nasal cavity, and roofs of orbits

Supraorbital foramen, frontal sinuses

Parietal (2)

Form side walls and roof of cranium

Fused at midline along sagittal suture

Occipital (1)

Forms back of skull and base of cranium

Foramen magnum, occipital condyles

Temporal (2)

Form side walls and floor of cranium

External auditory meatus, mandibular fossa, mastoid process, styloid process, zygomatic process

Sphenoid (1)

Forms parts of base of cranium, sides of skull, and floors and sides of orbits

Sella turcica, sphenoidal sinuses

Ethmoid (1)

Forms parts of roof and walls of nasal cavity, floor of cranium, and walls of orbits

Cribriform plates, perpendicular plate, superior and middle nasal conchae, ethmoidal sinuses, crista galli

and the base of the cranium. A large opening on its lower surface, the foramen magnum, houses nerve fibers from the brain that pass through and enter the vertebral canal to become part of the spinal cord. Rounded processes called occipital condyles, located on each side of the foramen magnum, articulate with the first vertebra (atlas) of the vertebral column.

4. Temporal bones. A temporal (tem'por-al) bone on each side of the skull joins the parietal bone along a squamosal (skwa-mo'sal) suture. The temporal bones form parts of the sides and the base of the cranium. Located near the inferior margin is an opening, the external auditory (acoustic) meatus, which leads inward to parts of the ear. The temporal bones also house the internal ear structures and have depressions called the mandibular fossae (glenoid fossae) that articulate with condyles of the mandible. Below each external auditory meatus are two projections—a rounded mastoid process and a long, pointed styloid process. The mastoid process provides an attachment for certain muscles of the neck, whereas the styloid process anchors muscles associated with the tongue and pharynx. An opening near the mastoid process, the carotid canal, transmits the internal carotid artery. An opening between the temporal and occipital bones, the jugular foramen, accommodates the internal jugular vein (see fig. 7.22).

A zygomatic process projects anteriorly from the temporal bone in the region of the external auditory meatus. It joins the zygomatic bone and helps form the prominence of the cheek.

5. Sphenoid bone. The sphenoid (sfe'noid) bone (fig. 7.23) is wedged between several other bones in the anterior portion of the cranium. It consists of a central part and two winglike structures that extend laterally toward each side of the skull. This bone helps form the base of the cranium, the sides of the skull, and the floors and sides of the orbits. Along the midline within the cranial cavity, a portion of the sphenoid bone indents to form the saddle-shaped sella turcica (sel'ah tur'si-ka). In this depression lies the pituitary gland, which hangs from the base of the brain by a stalk.

The sphenoid bone also contains two sphenoidal sinuses. These lie side by side and are separated by a bony septum that projects downward into the nasal cavity.

6. Ethmoid bone. The ethmoid (eth'moid) bone

(fig. 7.24) is located in front of the sphenoid bone. It consists of two masses, one on each side of the nasal cavity, which are joined horizontally by thin cribriform (krib'ri-form) plates. These plates form part of the roof of the nasal cavity, and nerves associated with the sense of smell pass through tiny openings (olfactory foramina) in them. Portions of the ethmoid bone also form sections of the cranial floor, orbital walls, and nasal cavity walls. A perpendicular plate projects downward in the midline from the cribriform plates to form most of the nasal septum.

Delicate, scroll-shaped plates called the superior nasal concha (kong'kah) and the middle nasal concha project inward from the lateral portions of the ethmoid bone toward the perpendicular plate. These bony plates support mucous membranes that line the nasal cavity. The mucous membranes, in turn, begin moistening, warming, and filtering air as it enters the respiratory tract. The lateral portions of the ethmoid bone contain many small air spaces, the ethmoidal sinuses. Figure 7.25 shows various structures in the nasal cavity.

Projecting upward into the cranial cavity between the cribriform plates is a triangular process of the ethmoid bone called the crista galli (kris'tai gal'li; cock's comb). Membranes that enclose the brain attach to this process. Figure 7.26 shows a view of the cranial cavity.

Trepanation was an early treatment in many cultures in the Old and New World. The procedure involves drilling holes in the skull and sometimes removing pieces of cranium. Trepanation was used for physical ailments, such as fractures, or for spiritual ills, such as headaches, seizures, and mental disorders. Early evidence of trepanation is a male skull from about 7,000 years ago found in a Neolithic burial site in Alsace. The skull contained two drill holes, one in the frontal bone, the other covering both parietal bones. New bone had formed a thin shell over the smaller, anterior lesion and had partially covered the larger hole. The fact that the man lived to the old age of fifty-five attests to the skill of the long-ago surgeon. Neanderthals, who lived 20,000 to 30,000 years ago, also used trepanation. Modern researchers used CT scans to identify the trepanation, which can superficially resemble fractures or mauling of a skull after death.

Facial Skeleton

The facial skeleton consists of thirteen immovable bones and a movable lower jawbone. In addition to forming the basic shape of the face, these bones provide attachments for muscles that move the jaw and control facial expressions.

The bones of the facial skeleton are as follows:

1. Maxillary bones. The maxillary (mak'si-ler"e) bones (pl., maxillae, mak-sll'e) form the upper jaw;

The mastoid process may become infected. The tissues in this region of the temporal bone contain a number of interconnected air cells lined with mucous membranes that communicate with the middle ear. These spaces sometimes become inflamed when microorganisms spread into them from an infected middle ear {otitis media). The resulting mastoid infection, called mastoid-itis, is of particular concern because nearby membranes that surround the brain may become infected.

Lesser wing Optic canal

Greater wing (a)

Lesser wing Optic canal

Greater wing (a)

Agujero Pelvico

Transverse section

Transverse section

Greater wing

Superior orbital fissure

Foramen rotundum

Lateral pterygoid plate Medial pterygoid plate

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