Foramina of the Skull
Gross Anatomy
SKULL DEVELOPMENT
In basic terms, the skull is made up of two sets of bones which begin to develop
early in utero. The neurocranium consists of the bones forming a protective case
around the brain and the viscerocranium consists of the bones of the face.
Osteogenesis of the skull (bone development) begins in the 7th/8th weeks of fetal life
and continues into adulthood. Osteogenesis occurs by both endochondral and
intramembranous ossification.
NEUROCRANIUM
The neurocranium surrounds the brain creating the cranial vault and consists of 8 flat
bones including the parietal (2), temporal (2), frontal, occipital and ethmoid bones
(Figure 1). However, the bones are in fact curved in shape - convex externally and
concave internally.
Calvaria:

Superior aspect of the neurocranium – Roof/Skullcap
The flat bones of the roof are formed by intramembranous ossification of neural crest
cells, creating the membranous neurocranium. The membranous portion of the
skull surrounds the brain creating a protective vault.
Ossification of the skull is not complete at the time of birth and the bones of the skull
articulate via sutures or fontanelles (non-ossified articulations). Fontanelles are
spaces between the cranial bones that are filled with fibrous membranes. This is
required during childbirth as the flexibility of the sutures and fontanelles allows the
bones to overlap so the baby's head can pass through the birth canal, without
compressing and damaging the brain. The sutures remain flexible during childhood
Foramina of the Skull
to allow the brain to grow. As brain growth and expansion occurs, the separate
bones of the calvaria are displaced in an outward direction. This creates tension at
the sutures and fontanelles promoting bone deposition, which continues as the brain
continues to develop and grow. This continues until the 4th year of life, when the
bones of the cranium are united by fibrous and hyaline cartilage sutures.
Cranial base:

Inferior aspect of the neurocranium – Floor
The cranial base consists mainly of the sphenoid, temporal and occipital bones
which are formed by endochondral ossification of cartilage creating cartilaginous
neurocranium (chondrocranium).
Figure 1. (a) Superior view of cranial base of the neurocranium. (b) Lateral view
of skull. Area superior to the red line shows the calvaria of the neurocranium.
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VISCEROCRANIUM
The viscerocranium is situated anterior to the neurocranium and is comprised of 14
irregular bones including 6 pairs of bones:
1. Zygomatic (x2)
2. Palatine (x2)
3. Nasal (x2)
4. Lacrimal (x2)
5. Maxilla (x2)
6. Inferior nasal concha (x2)
7. Mandible
8. Ethmoid
The viscerocranium develops in the mesenchyme (neural crest cells from which the
calvaria of the neurocranium is also derived) or sclerotome (derived from mesoderm)
of the 1st and 2nd embryonic pharyngeal arches. The bones of the viscerocranium
create what is commonly referred to as the facial skeleton (Figure 2).
Within commonly used texts there is debate as to which bones are included in the
facial skeleton (viscerocranium). Some make a distinction between the bones of the
skull based on the embryological origins. Other texts include all the bones that can
be seen on an anterior view of the skull as part of the . As a result, it is not
uncommon to see the frontal, hyoid, parietal and sphenoid bones described as part
of the facial skeleton.
Foramina of the Skull
Figure 2. (a) Anterior view of the facial bones of the skull (viscerocranium). (b)
Inferior view of the skull base with mandible removed showing the relations of
the bones of the viscerocranium and neurocranium.
CRANIAL FOSSAE
The internal surface of the neurocranium base has 3 depressions which create the
bowl shape of the cranial cavity that accommodate the brain. Figure 2 displays the 3
depressions/fossae. The fossae increase in depth from anterior to posterior and are
termed the:
1. Anterior cranial fossa
2. Middle cranial fossa
3. Posterior cranial fossa
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Figure 2. (a) Lateral view of cranial fossae of the adult skull with brain in situ.
(b) Superior view of cranial fossae of adult skull with brain removed.
ANTERIOR CRANIAL FOSSA
The anterior fossa is formed from the frontal bone anteriorly, the ethmoid bone in the
midline and the body and the lesser wings of the sphenoid bone posteriorly (Figure
3). Two skull foramina located in the anterior fossa:
1. Foramen caecum
2. Foramen of the cribriform plate
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Figure 3. (a) Superior view of the skull base with the anterior cranial fossa
highlighted in green. (b) Bones that form the anterior cranial fossa.
MIDDLE CRANIAL FOSSA
The middle cranial fossa is butterfly shaped and is located posteroinferior to the
anterior fossa (Figure 4). Both the greater wings of the sphenoid and temporal bone
create the lateral sections of the fossa. The middle cranial fossa contains 6 foramina:
1. Optic canal
2. Superior orbital fissure
3. Foramen rotundum
4. Foramen ovale
5. Foramen spinosum
6. Foramen lacerum
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Figure 4. (a) Superior view of the skull base with the middle cranial fossa
highlighted in orange. (b) Bones that form the middle cranial fossa.
POSTERIOR CRANIAL FOSSA
The posterior fossa is the largest and deepest of the 3 fossae. The occipital bone is
the main contributor to the fossa and the temporal bone forms the antero-lateral
boundaries (Figure 5). There are 4 foramina found in the posterior cranial fossa:
1. Internal acoustic meatus
2. Jugular foramen
3. Hypoglossal canal
4. Foramen magnum
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Figure 5. (a) Superior view of the skull base with the posterior cranial fossa
highlighted in red. (b) Bones that form the posterior cranial fossa.
IMAGES AND TABLES OF NEUROCRANIUM FORAMINA AND CONTENTS
Figure 6. Superior view of the cranial cavity with the brain removed and the
foramina of the neurocranium highlighted.
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Figure 7. Inferior view of the skull base with the mandible removed and
neurocranium foramina highlighted.
Table 1. Overview of the foramina found in the anterior cranial fossa and the
foramina contents.
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Table 2. Overview of the foramina found in the middle cranial fossa and the
foramina contents.
Table 3. Overview of the foramina found in the posterior cranial fossa and the
foramina contents.
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VISCEROCRANIUM FORAMINA
Forming the anterior part of the cranium, the viscerocranium region has 7 foramina
that allow structures to enter and exit the cranial cavity. The bones of the
viscerocranium surround the mouth, nasal cavity and orbit. A branch of the trigeminal
nerve is found in each foramina - highlighting the importance of the trigeminal (CN V)
nerve in facial innervation.
Read through the Table 4, which summarises the foramina and the key structures.
Use Figures 8 and 9 to aid your understanding of the foramina location.
Table 4. Overview of the foramina found in the facial bones of the skull and the
foramina contents.
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Figure 8. Foramina of the viscerocranium region of the skull. (Not depicted is
the mandibular foramen as it is located on the posterior surface of the
mandible)
Figure 9. Lateral view of adult skull showing foramina and nerve contents of
viscerocranium.
Foramina of the Skull