6-1e Cranial Bones

Within the cranial bones of a newborn are two points of union where a space is present between the bones. These spaces are called fontanelles ("soft spots"), also spelled

-fontanel A fontanelle is a space between bones of an infant's cranium that is covered by a tough membrane.

parietal bones (pah-REYE-eh-tal)

Moving toward the back of the head, just behind the frontal bones ("posterior to the frontal bones") are the two parietal bones. They form most of the top and the upper sides of the cranium.

sutures

The borders of the cranial bones meet to form sutures, or immovable joints.

ethmoid bone (ETH-moyd)

The ethmoid bone lies just behind the nasal bone, in front of the sphenoid bone. It also forms the front of the base of the skull, part of the eye orbits, and the nasal cavity. The ethmoid bone also contains the ethmoid sinuses.

Facial Bones

The facial part of the skull is given its distinctive shape by two bones: the maxillae (upper jaw bones) and the mandible (lower jaw bone). These bones and 12 others make up the facial bones. All of the facial bones are connected by immovable joints (sutures) with the exception of the mandible (the only movable joint of the skull). Refer to Figure 6-5 as you study the facial bones.

The fontanelles in a newborn:

The fontanelles in the newborn permit the bones of the roof of the skull to override one another during the birth process, narrowing the skull slightly as the head is exposed to the pressures within the birth canal. This may mold the newborn's head into an asymmetrical shape during the birthing process. The head generally assumes its normal shape in a week. The complete ossification of the cranial sutures (making them immovable joints) does not occur for some years after birth. The cranial bones are held together by fibrous connective tissue until ossification occurs, allowing some movement of the infant's skull bones. This feature permits additional growth of the skull to accommodate the normal development of the brain.

frontal bone

The frontal bone forms the forehead (front of the skull) and the upper part of the bony cavities that contain the eyeballs. The frontal sinuses are located in this bone, just above the area where the frontal bone joins the nasal bones.

hyoid bone

The hyoid (HIGH-oyd) bone is located just above the larynx and below the mandible (see Figure 6-6). It does not connect with any other bone to form a joint but is suspended from the temporal bone by ligaments. The hyoid bone serves as points of attachment for muscles of the tongue and throat.

mandibular bone (man-DIB-yoo-lar)

The mandibular bone, or mandible, is the lower jaw bone. It is the largest, strongest bone of the face and is the only movable bone of the skull. The mandibular bone meets the temporal bone in a movable joint called the temporomandibular joint, or TMJ. The mandible contains sockets for the teeth along its upper margin.

occipital bone (ock-SIP-ih-tal)

The single occipital bone forms the back of the head and the base of the skull (the back portion of the floor of the cranial cavity). The occipital bone contains the foramen magnum (a large opening in its base), through which the spinal cord passes.

sphenoid bone (SFEE-noyd) sphen/o = wedge -oid = resembling

The sphenoid bone is a bat-shaped bone (resembling a bat with outstretched wings) located at the base of the skull in front of the temporal bones. It extends completely across the middle of the cranial floor, joining with and anchoring the frontal, parietal, occipital, temporal, and ethmoid bones. The sphenoid bones form part of the base of the eye orbits.

nasal conchae (NAYZ-al KONG-kee)

The two inferior nasal conchae bones help complete the nasal cavity by forming the side and lower wall. These bones connect with the maxilla, lacrimal, ethmoid, and palatine bones.

maxillary bones (MACK-sih-ler-ee)

The two maxillary bones (maxillae) are the bones of the upper jaw. They are fused in the midline by a suture. These two bones form not only the upper jaw but the hard palate (front part of the roof of the mouth). The maxillary bones contain the maxillary sinuses and the sockets for the teeth along the lower margin.

palatine bones (PAL-ah-tine)

The two palatine bones are shaped like the letter L: they have a vertical and a horizontal portion. The vertical portion of the palatine bones forms the sidewall of the back of the nasal cavity. The horizontal portion of the palatine bones joins in the midline to form the back (posterior) part of the roof of the mouth, or hard palate. The palatine bones also join with the maxillae and sphenoid bone.

lacrimal bones (LACK-rim-al)

The two small lacrimal bones are paper thin and shaped somewhat like a fingernail. They are located at the inner corner of each eye, forming the sidewall of the nasal cavity and the middle wall of the eye orbit. The lacrimal bones join the cheek bones on each side to form the fossa, which houses the tear (or lacrimal) duct.

temporal bones (TEM-por-al)

The two temporal bones form the lower sides and part of the base of the skull (cranium). These bones contain the middle and inner ear structures. They also contain the mastoid sinuses. Immediately behind the external part of the ear is the temporal bone, which projects downward to form the (4a) mastoid process, which serves as a point of attachment for muscles.

zygomatic bones (zeye-go-MAT-ik)

The two zygomatic bones—one on each side of the face—form the high part of the cheek and the outer border of the eye orbits.

vomer (VOH-mer)

The vomer is a thin, flat bone that forms the lower portion of the nasal septum. It joins with the sphenoid, palatine, ethmoid, and maxillary bones. Other facial bones that are not shown in the illustration include the following:

anterior fontanelle, also called the frontal fontanelle

is the diamond-shaped space between the frontal and the parietal bones. It normally closes between 18 and 24 months of age.

posterior fontanelle, also called the occipital fontanelle

is the space between the occipital and parietal bones and is much smaller than the anterior fontanelle. It normally closes within 2 months after birth.