The skull II

Fig.55.1

The base of the skull from below

Incisive fossa

Horizontal plate of palatine

Vomer

Foramen lacerum

Tympanic plate Mastoid process

Occipital condyle Foramen magnum

Fig.55.1

The base of the skull from below

Palatal process of maxilla Greater palatine foramen

Pterygoid hamulus Lateral pterygoid plate Foramen ovale Foramen spinosum and spine of sphenoid Carotid canal Jugular foramen

Coronoid process

Course of lingual nerve

Coronoid process

Alveolar part of body

Body

The internal surface of the mandible

Head

Ramus

Mandibular foramen

Rough area for medial pterygoid

The outside of the base of the skull (Fig. 55.1) The anterior part of the cranial base is hidden by the bones of the face (p. 125). The remainder consists of the bones that were seen in the middle and posterior cranial fossae but many of the foramina seen on the exterior are not visible inside the cranium.

• Temporal (Squamous, petrous and tympanic parts and the styloid process)

• Sphenoid (body) which carries the medial and lateral pterygoid plates

• Foramen magnum (already described)

• Hypoglossal canal (already described)

• Stylomastoid foramen (facial nerve)

• Jugular foramen (already described)

• Foramen lacerum (the internal carotid through its internal opening)

• Carotid canal (internal carotid artery and sympathetic nerves)

• Foramen spinosum (already described)

• Foramen ovale (already described) • Other features:

• The area between and below the nuchal lines is for the attachment of the extensor muscles of the neck.

• The occipital condyles, for articulation with the atlas, lie on either side of the foramen magnum.

• The mastoid process is part of the petrous temporal and contains the mastoid air cells (p. 157).

• The floor of the external auditory meatus is formed by the tympanic plate of the temporal bone.

• The carotid canal (see Fig. 59.2) turns inside the temporal bone to run horizontally forwards. It then opens into the posterior wall of the foramen lacerum before turning upwards again to enter the cranial cavity through the internal opening of the foramen.

• Behind the foramen spinosum is the spine of the sphenoid which lies medial to the mandibular fossa for articulation with the head of the mandible.

• In front of this is the articular eminence, onto which the head of the mandible moves when the mouth is open.

The bones of the face (Figs 54.2 and 55.2)

The bones of the face are suspended below the front of the cranium and comprise the bones of the upper jaw, the bones around the orbit and nasal cavities and the mandible.

• Pterygoid plates of the sphenoid

• Bones of the orbit and nasal cavities (see below)

• Supraorbital (Supraorbital nerve)

• Infraorbital ( Infraorbital nerve)

• Greater and lesser palatine foramina (Greater and lesser palatine nerves)

• Foramina of the incisive fossa (Nasopalatine nerves and vessels) • Other features:

• The pterygoid plates of the sphenoid support the back of the maxilla.

• Between these two bones is the pterygomaxillary fissure which leads into the pterygopalatine fossa.

• The hard palate is formed by the palatine process of the maxilla and the horizontal plate of the palatine.

• The teeth are borne in the maxilla.

• The maxilla contains the large maxillary air sinus.

• The bones of the orbit: the orbital margins are formed by the frontal, zygomatic and maxillary bones.

• The ethmoid lies between the two orbits and contains the ethmoidal air cells.

• The lacrimal has a fossa for the lacrimal sac.

• At the back of the orbit are the greater and lesser wings of the sphenoid with the superior orbital fissure between them. Also the optic canal and the infraorbital fissure.

• The bones of the nasal cavity are the maxilla, the inferior concha, the ethmoid, the vomer, the nasal septum and the perpendicular plate of the palatine.

The mandible (Fig. 55.2) consists of the body and two rami. Each ramus divides into a coronoid process and the head, for articulation with the mandibular fossa. The mandibular foramen transmits the inferior alveolar nerve and vessels.

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