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.
All bones seen in N. Lateralis. Click on the image for labels.
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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.
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
The mandible presents many important landmarks in a lateral view of the skull.
The mental protuberance is the point of the chin
The body of the mandible is the horizontal portion of the bone, bearing the inferior alveolar arch and the lower teeth.
The ramus of the mandible is the vertical portion of the bone.
The mandibular angle is formed by the intersection of body and ramus.
The coronoid process is the anterior upward projection from the ramus that gives attachment to the temporalis muscle.
The condylar or articular process is the posterior upward projection of the mandibular ramus.
The neck of the mandible is the lower, narrower portion of the articular process.
The head of the mandible is the expanded upper extremity of the articular process, above the neck. In life it is covered by hyaline cartilage.
The temporomandibular joint (TMJ) is formed between the head of the mandible and the mandibular (glenoid) fossa on the under surface of the temporal bone.
The mandibular notch lies between the coronoid and condylar processes. It gives access to the infratemporal fossa, which will be described separately.