The Skull in Infancy and Childhood

The head of an infant could not fit through the mother's pelvic outlet at birth were it not for the fact that the bones of its skull are not yet fused. The shifting of the skull bones during birth may cause the infant to appear deformed, but the head soon assumes a more normal shape. Spaces between the unfused cranial bones are called fontanels,32 after the fact that pulsation of the infant's blood can be felt there. The bones are joined at these points only by fibrous membranes, in which intramembranous ossification will be completed later. Four of these sites are especially prominent and regular in location: the anterior, posterior, sphenoid (anterolateral), and mastoid (posterolateral) fontanels (fig. 8.17). Most fontanels ossify by the time the infant is a year old, but the largest one—the anterior fontanel—can still be palpated 18 to 24 months after birth.

The frontal bone and mandible are separate right and left bones at birth, but fuse medially in early childhood. The frontal bones usually fuse by age five or six, but in

Fetal Skull Sutures
Figure 8.17 The Fetal Skull Near the Time of Birth. (a) Right lateral view; (b) superior view.

some children a metopic33 suture persists between them. Traces of this suture are evident in some adult skulls.

The face of a newborn is flat and the cranium relatively large. To accommodate the growing brain, the skull grows more rapidly than the rest of the skeleton during childhood. It reaches about half its adult size by 9 months of age, three-quarters by age 2, and nearly final size by 8 or 9 years. The heads of babies and children are therefore much larger in proportion to the trunk than the heads of adults—an attribute thoroughly exploited by cartoonists and advertisers who draw big-headed characters to give them a more endearing or immature appearance. In humans and other animals, the large rounded heads of the young are thought to promote survival by stimulating parental caregiving instincts.

Table 8.4 summarizes the bones of the skull.

31 cornu = horn

32fontan = fountain + el = little

Saladin: Anatomy & I 8. The Skeletal System I Text I © The McGraw-Hill

Physiology: The Unity of Companies, 2003 Form and Function, Third Edition

Table 8.4 Anatomical Checklist for the Skull and Associated Bones

Cranial Bones

Table 8.4 Anatomical Checklist for the Skull and Associated Bones

Cranial Bones

Frontal Bone (figs. 8.4 to 8.7)

Occipital Bone (figs. 8.4,8.5, and 8.6)—(Cont.)

Supraorbital margin

Condylar canal

Supraorbital foramen or notch

External occipital protuberance

Glabella

Superior nuchal line

Frontal sinus

Inferior nuchal line

Parietal Bones (figs. 8.4a and 8.6)

Sphenoid Bone (figs. 8.4a, 8.5, and 8.11)

Temporal lines

Body

Parietal foramen

Lesser wing

Temporal Bones (figs. 8.4,8.5b, and 8.10)

Optic foramen

Squamous part

Anterior clinoid process

Zygomatic process

Superior orbital fissure

Mandibular fossa

Greater wing

Tympanic part

Foramen ovale

External auditory meatus

Foramen rotundum

Styloid process

Foramen spinosum

Mastoid part

Foramen lacerum

Mastoid process

Medial and lateral pterygoid plates

Mastoid notch

Nasal choanae

Mastoid foramen

Sphenoid sinus

Stylomastoid foramen

Sella turcica

Petrous part

Dorsum sellae

Internal auditory meatus

Ethmoid Bone (figs. 8.4,8.7, and 8.12)

Carotid canal

Perpendicular plate

Jugular foramen

Superior nasal concha (superior turbinate bone)

Occipital Bone (figs. 8.4,8.5, and 8.6)

Middle nasal concha (middle turbinate bone)

Foramen magnum

Ethmoid sinus (air cells)

Basilar part

Crista galli

Occipital condyles

Cribriform plate

Hypoglossal canal

Facial Bones

Maxilla (figs. 8.3,8.4, and 8.5a)

Nasal Bones (figs. 8.3 and 8.13)

Alveoli

Inferior Nasal Concha (fig. 8.13)

Alveolar processes

Vomer (figs. 8.3 and 8.4b)

Infraorbital foramen

Mandible (figs. 8.3 and 8.15)

Inferior orbital fissure

Body

Palatine processes

Mental symphysis

Incisive foramen

Mental protuberance

Maxillary sinus

Mental foramen

Palatine Bones (figs. 8.5a and 8.13)

Angle

Greater palatine foramen

Ramus

Zygomatic Bones (figs. 8.4a and 8.5a)

Condyloid process

Zygomaticofacial foramen

Mandibular condyle

Temporal process

Coronoid process

Lacrimal Bones (figs. 8.3 and 8.14)

Mandibular notch

Lacrimal fossa

Mandibular foramen

Bones Associated with the Skull

Auditory Ossicles

Hyoid Bone (fig. 8.16)

Malleus (hammer)

Body

Incus (anvil)

Greater cornu

Stapes (stirrup)

Lesser cornu

Saladin: Anatomy & I 8. The Skeletal System I Text I © The McGraw-Hill

Physiology: The Unity of Companies, 2003 Form and Function, Third Edition

262 Part Two Support and Movement

Insight 8.3 Clinical Application

Cranial Assessment of the Newborn

Obstetric nurses routinely assess the fontanels of newborns by palpation. In a difficult delivery, one cranial bone may override another along a suture line, which calls for close monitoring of the infant. Abnormally wide sutures may indicate hydrocephalus, the accumulation of excessive amounts of cerebrospinal fluid, which causes the cranium to swell. Bulging fontanels suggest abnormally high intracranial pressure, while depressed fontanels indicate dehydration.

Before You Go On

Answer the following questions to test your understanding of the preceding section:

  1. Name the paranasal sinuses and state their locations. Name any four other cavities in the skull.
  2. Explain the difference between a cranial bone and a facial bone. Give four examples of each.
  3. Draw an oval representing a superior view of the calvaria. Draw lines representing the coronal, lambdoid, and sagittal sutures. Label the four bones separated by these sutures.
  4. State which bone has each of these features: a squamous part, hypoglossal foramen, greater cornu, greater wing, condyloid process, and cribriform plate.
  5. For each of the following bones, name all the other bones with which it articulates: parietal, temporal, zygomatic, and ethmoid.
  6. Determine which of the following structures cannot normally be palpated on a living person: the mastoid process, crista galli, superior orbital fissure, palatine processes, zygomatic bone, mental protuberance, and stapes. You may find it useful to palpate some of these on your own skull as you try to answer.

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Responses

  • tommy
    How are the sutures of an adult different from fetal skull?
    7 years ago
  • tanta proudfoot
    Where is anterolateral fontal in a infant?
    7 years ago
  • Klaudia
    What are functions of the bones of the fetal skull?
    7 years ago
  • Bisrat
    How can we different the foetal skull from normal adult skull?
    3 years ago

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