HUMAN ANATOMY ATLAS - G.L. Bilich - 2014

APPARATUS OF LOCOMOTION

SKELETAL SYSTEM

SKULL OF THE NEWBORN AND AGE-RELATED FEATURES OF THE SKULL

The most characteristic feature of the newborn skull is the fontanelles (fonticuli), which are unossified connective tissue (membranous) areas of the cranial vault. There are six fontanelles in total: two located along the midline of the cranial roof and four on its lateral surfaces. The largest is the anterior (frontal) fontanelle (fonticulus anterior, s. frontalis), which is diamond-shaped and situated between the two halves of the frontal bone anteriorly and the two parietal bones posteriorly; it closes during the second year of life. The posterior (occipital) fontanelle (fonticulus posterior, s. occipitalis) is triangular in shape, located between the two parietal bones anteriorly and the occipital squama posteriorly. The occipital fontanelle closes by the second month after birth. The anterolateral fontanelle, or sphenoid fontanelle (fonticulus sphenoidalis), is found at the junction of the frontal, parietal, temporal squama, and the greater wing of the Sphenoid bone. This fontanelle closes by the second to third month after birth. The posterolateral fontanelle, or mastoid fontanelle (fonticulus mastoideus), is located at the intersection of the temporal, occipital, and parietal bones, and closes by the second to third month of life.

Due to the presence of fontanelles, the newborn skull is elastic, and its shape can change as the fetal HEAD passes through the mother's birth canal. Overlapping of the cranial vault bones is also possible, which reduces the dimensions of The Skull and facilitates childbirth. This is facilitated by Budin's plate—a cartilaginous plate located in the fetus between the lateral part of the Occipital bone and its squama, which allows the bones to slide and override one another during labor. An accessory bone, known as Vesalius' bone or the bone of the anterior fontanelle (os fonticuli anterioris), frequently forms at the site of the anterior fontanelle.

The volume of the cranial cavity in a newborn averages 385–450 cm³. During the first 6 months after birth, the cranial cavity volume doubles, by two years it triples, and in an adult it is four times greater than that of a newborn. The glabella is absent in the newborn and develops by the age of 15. The Proportions of the neurocranium and viscerocranium differ between adults and newborns. The newborn's face is short and wide. In lateral norm, The ratio of the facial to the cranial areas in a newborn is 1:8, in a two-year-old child 1:6, in a five-year-old 1:4, in a ten-year-old 1:3, in an adult female 1:2.5, and in an adult male 1:2.

After birth, skull growth occurs unevenly; consequently, three periods of postnatal GROWTH AND DEVELOPMENT are distinguished.

The first period—from birth to 7 years of age—is characterized by rapid growth, particularly in the occipital region of the skull. During the first year of life, the skull grows more or less evenly. From 1 to 3 years of age, the skull experiences particularly active posterior growth, which is associated with the child's transition to bipedal Locomotion in the second year of life. During the second and third years, coinciding with the completion of deciduous dentition eruption and increased masticatory Muscle Function, the height and width of the facial skeleton increase significantly. From 3 to 7 years of age, the entire skull continues to grow, especially its base. By age 7, longitudinal growth of the cranial base is largely complete, reaching a size nearly equivalent to that of an adult.

The second period—from 7 years to the onset of Puberty (12–13 years)—is characterized by slowed but steady skull growth, particularly in the cranial base. During this time, the cranial vault grows primarily, especially up to age 8 and again between 11 and 13 years. The volume of the cranial cavity reaches 1200–1300 cm³. By age 13, the sphenosquamosal (squamomastoid) suture closes, and the fusion of separate bone parts developing from independent ossification centers is complete.

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Fig. 82. Newborn skull, fontanelles (A — anterior view, B — lateral view, right):

1 — Mandibtilarsymphysis; 2 — Milktooth; 3 — Infra-orbital foramen; 4 — Bony nasal septum; 5 — Sphenoid; Sphenoidal bone, greaterwing; 6 — Nasal bone; 7 — Maxilla, frontal process; 8 — Frontal bone; Frontal tuber; Frontal eminence; 9 — Frontal suture; Metopic suture; 10 — Anterior fontanelle; 11 — Parietal bone; 12 — Coronal suture; 13 — Supra-orbital notch/foramen; 14 — Maxilla; 15 — Temporal bone; 16 — Zygomatic bone; 17 — Mandible; 18 — Mental foramen; 19 — Occipital bone, lateral part; 20 — Mastoid fontanelle; 21 — Lambdoid suture; 22— Squamous part of occipital bone; 23— Posterior fontanelle; 24 — Temporal bone, petrouspart; 25 — Parietal bone; Parietal tuber; Parietal eminence; 26 — Sphenoidal fontanelle; 27 — Piriform aperture; 28 — Temporal bone, squamous part: 29 — Tympanio ring

Fig. 83. Newborn skull, fontanelles (A — superior view, B — inferior view):

1 — Occipital bone, squamous part of occipital bone; 2— Lambdoid suture; 3 — Sagittal suture; 4 — Anterior fontanelle; 5 — Frontal suture; Metopic suture; 6 — Frontal bone; squamous part; 7— Corona! suture; 8— Parietal bone; Parietal tuber; Parietal cminence; 9 — Posterior fontanelle; 10 — Palatine bone, horizonta! piate; 11— Vomer; 12 — Sphenoid; Sphenoidal bone, pterygoid process; 13 — Temporal bone, petrous part; 14 — Temporal bone, squamous part; 15 — Tympanio part, tympanic ring; 16 — Mastoid fontanelle; 17 — Transverse occipital suture; 18 — Occipital bone, lateral part; 19 — Foramen magnum; 20— Choana; Posterior nasal aperture; 21 — Maxilla, palatine process; 22— Incisive bone; Premaxilla; 23 — Mandible

During the third period—from 13 to 20–23 years of age—the facial skeleton undergoes intensive growth, and Sexual Dimorphism becomes apparent: in boys, the facial skeleton grows more in length than in girls, resulting in a more elongated face. While the face is rounded in both boys and girls prior to puberty, following puberty it typically elongates in males, whereas in females it retains its rounded contour.

The remodeling of Cranial bones in middle and old age can be attributed to the fourth period. During this time, the sutures between the BONES OF THE cranial vault undergo synostosis (closure). Cranial suture closure begins between the ages of 20 and 30, occurring slightly earlier in men than in women. The sagittal suture is the first to close in its posterior region (at 22–35 years), followed by the coronal suture (24–42 years), the lambdoid suture (26–42 years), and the occipitomastoid suture (30–81 years). The squamous suture generally remains open. The timing of suture obliteration is highly individual, and cases are known where all sutures remained distinct in elderly individuals over the age of 80.

In elderly and senile individuals, structural Changes in the viscerocranium occur alongside suture closure. Due to tooth wear and loss, the alveolar processes of the maxilla and mandible (alveolar arches) undergo resorption and diminish in size. As a result of reduced masticatory function and partial Atrophy of the Muscles of Mastication, the bony contours of the jaws become smoothed out and less massive. The cranial bones also become thinner and more brittle.