Anatomy of the Face - Flipbook - Page 33
Bones of the Skull
The cranium (Latin term for skull) is the most cephalad aspect of the axial skeleton. It is composed of 22 bones divided into two
regions: the neurocranium (which protects the brain) and the viscerocranium (which forms the face). The skull also supports
tendinous muscle attachments and allows neurovascular passage between intracranial and extracranial anatomy. The skull is
embryologically derived from mesoderm and neural crest and will fuse, harden, and mold from gestation through adulthood via
cranial sutures (fibrous joints) to protect its inner contents: the cerebrum, cerebellum, brainstem, and orbits. It gives the human
face its form, and even minor variations in anatomy among individuals can lead to wide differences in appearance. Various
foramina, condyles, and other bony landmarks provide passageways and attachments for the important structures associated
with the skull. It supports the muscles of the face and scalp by providing muscular and tendinous attachments, protects
neurovascular structures, and houses various sinuses to accommodate increases in pressure. Due to its complex development
and associated important structures, understanding skull anatomy holds abundant clinical and surgical significance.
CRANIUM
The cranium (also known as the neurocranium) is formed by the superior aspect of the skull. It encloses and protects the brain,
meninges, and cerebral vasculature.
Anatomically, the cranium can be subdivided into a roof and a base:
Cranial roof – comprised of the frontal, occipital and two parietal bones. It is also known as the calvarium.
Cranial base – comprised of six bones: frontal, sphenoid, ethmoid, occipital, parietal and temporal. These bones articulate with
the 1st cervical vertebra (atlas), the facial bones, and the mandible (jaw).
FACE
The facial skeleton (also known as the viscerocranium) supports the soft tissues of the face.
It consists of 14 bones, which fuse to house the orbits of the eyes, the nasal and oral cavities, and the sinuses. The frontal bone,
typically a bone of the calvaria, is sometimes included as part of the facial skeleton.
The facial bones are:
Zygomatic (2) – forms the cheek bones of the face and articulates with the frontal, sphenoid, temporal and maxilla bones.
Lacrimal (2) – the smallest bones of the face. They form part of the medial wall of the orbit.
Nasal (2) – two slender bones that are located at the bridge of the nose.
Inferior nasal conchae (2) – located within the nasal cavity, these bones increase the surface area of the nasal cavity, thus
increasing the amount of inspired air that can come into contact with the cavity walls.
Palatine (2) – situated at the rear of oral cavity and forms part of the hard palate.
Maxilla (2) – comprises part of the upper jaw and hard palate.
Vomer – forms the posterior aspect of the nasal septum.
Mandible (jaw) – articulates with the base of the cranium at the temporomandibular joint (TMJ).
SUTURES OF THE SKULL
Sutures are a type of fibrous joint that are unique to the skull. The sutures of the skull allow for movement of the cranial bones
during infancy, and this persists into adulthood. Eventually, these sutures fuse and are no longer moveable. There is a great deal
of variation in the timing of the closure of individual sutures. The sagittal suture closes first around age 22, then the coronal
suture, followed by the lambdoid around age 26, and the squamous sutures around age 60. The metopic suture splits the frontal
bones and typically closes at three months of age but can take up to 9 months.
These joints are important in the context of trauma, as they represent points of potential weakness in the skull. The main sutures in
the adult skull are:
•
Coronal suture – fuses the frontal bone with the two parietal bones.
•
Sagittal suture – fuses both parietal bones to each other.
•
Lambdoid suture – fuses the occipital bone to the two parietal bones.
CRANIAL FONTANELLES
In neonates, the incompletely fused suture joints give rise to membranous gaps between the bones, known as fontanelles.
Fontanelles are soft areas where the skull has not ossified to allow for brain growth and development. There are six fontanelles,
with the anterior and posterior being the most prominent and clinically significant. The two major fontanelles are:
•
Frontal fontanelle – located at the junction of the coronal and sagittal sutures. The anterior fontanelle closes around
age 1-2 and hardens to become the bregma and adjacent coronal suture.
•
Occipital fontanelle – located at the junction of the sagittal and lambdoid sutures. The posterior fontanelle closes
around 6-8 weeks of age and becomes the lambda and adjacent lambdoid suture.
In this book we will cover the most prominent bones of the skull which are essential for understanding the anatomy of the face.
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