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Anatomy of the Skull: Norma Lateralis

The norma lateralis includes the lateral wall of the skull (the temple), the prominence of the cheek, the zygoma or zygomatic arch (Gr. Zygoun=bar, yoke), the external auditory meatus , the orbital and anterior nasal apertures in profile, the upper and lower jaws, the joint between the lower jaw and the base of the skull, the temporal fossa, the indentation in the lateral wall of the skull above the level of the zygomatic arch, and the infratemporal fossa, below the zygomatic arch and beneath the base of the skull. In a lateral view of the skull, the infratemporal fossa can be viewed only through the window between the zygomatic arch and the upper border of the mandible; it will be described separately.

BONES:

The frontal bone forms the forehead and superior orbital margin. It contributes to the wall and dome of the skull and to the anterior wall of the temporal fossa.

The parietal bone contributes to the wall and dome of the skull and to the wall of the temporal fossa.

The occipital bone forms the posterior wall of the skull.

The temporal bone forms the external auditory meatus. It contributes to the lateral wall of the skull, wall of the temporal fossa, and zygomatic arch.

The sphenoid bone contributes to the lateral wall of the skull and to the wall of the temporal fossa.

The zygomatic bone forms the prominence of the cheek, the lateral orbital margin, and the anterior wall of the temporal fossa. It contributes to the inferior orbital margin and the zygomatic arch.

The maxilla forms the upper jaw, the lateral margin of the nasal aperture and the medial margin of the orbit. It contributes to the inferior orbital margin.

The mandible forms the lower jaw.
All bones seen in N. Lateralis. Click on the image for labels.

Return to first (zoomable) view

PRINCIPAL SUTURES:

Frontonasal

Coronal

Lambdoidal

Parietotemporal

Sphenoparietal

Sphenofrontal

Zygomaticofrontal

Zygomaticomaxillary

Zygomaticotemporal

Nasomaxillary

Occipitomastoid

Parietomastoid

NEUROVASCULAR EXIT PORTALS:

The mandibular notch, between the mandible and the zygomatic process allows passage of the masseteric nerve and vessels. The nerve is a branch of the mandibular division of the trigeminal (V3). The artery is a branch of the 2nd part of the maxillary artery and belongs to the external carotid system; the vein drains to the pterygoid venous plexus and thence to the maxillary vein.

PROMINENT LANDMARKS AND REFERENCE POINTS:

The anterior nasal spine marks the union of left and right maxillae. It can be palpated easily on the midline in the lower part of the nasal septum

Nasion is the point of intersection of the frontonasal and internasal sutures.

Glabella (L. glaber=smooth, bald) is the smooth median elevation of the frontal bone linking the superciliary ridges.

Bregma (Gr.=”front of the head”) is the point of intersection of the coronal and sagittal sutures. This was the site of the anterior fontanelle.

The vertex is the highest point of the skull in the midline.

Lambda is the point of intersection of the sagittal and lambdoidal sutures. This was the site of the posterior fontanelle.

The external occipital protuberance is a midline elevation on the occipital bone. Inion (Gr.=”back of the head”) is the most prominent point of the external occipital protuberance.

The mastoid process (Gr. mastos=breast; breast-like) of the temporal bone is not present at birth. It is raised gradually by the pull of the sternocleidomastoid muscle once the infant has begun to lift its head. The process is filled with a system of air cells created by extensions of the lining of the middle ear cavity, with which they remain continuous.

The styloid process (Gr. stylos=pillar) of the temporal bone varies greatly in length from individual to individual. It is easily broken and may be missing in many prepared skulls.

The temporal lines are two bony ridges, convex upward, curving across the lateral aspect of the skull. The inferior temporal line marks the upper limit of the attachment of the temporalis muscle; the superior temporal line marks the attachment of the dense temporal fascia that covers the muscle.

Pterion (Gr. pteron, pteryx=a wing) is the region in which the frontal, parietal, and temporal bones all converge on the greater wing of the sphenoid bone. Here the wall of the temporal fossa is relatively thin and is weakened by the presence of numerous sutures. It is, therefore, easily fractured, and bone fragments may tear the underlying middle meningeal artery producing an epidural hematoma.

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