Page 336 - Clinical Anatomy

ECA5 7/18/06 6:51 PM Page 321

The mandible 321

cribiform plate and are related above to the frontal lobes of the brain. These
cells drain into the superior and middle meatus (Fig. 225).

Clinical features

As with the frontal sinus, infection (ethmoiditis) may result in a frontal
cerebral abscess and an ethmoidal fracture may cause a C.S.F. leakage into
the nasal cavity.

The sphenoid sinuses

These lie one on either side of the midline, within the body of the sphenoid
(Fig. 225). They vary a good deal in size and may extend laterally into the
greater wing of the sphenoid or backwards into the basal part of the occipi-
tal bone.
Each sinus drains into the nasal cavity above the superior concha (the
sphenoethmoidal recess).

Clinical features

The pituitary gland may be excised through a fibre-optic transnasal,
transsphenoidal approach in patients with pituitary tumour.

The mandible (Fig. 227)

The lower jaw comprises a horizontal body on each side which fuses at the
symphysis menti (fusion occurring at the 2nd year). From the posterior part
of the body projects the vertical ramus which bears an anterior coronoid and
a posterior condyloid process, made up of the head and neck. Between the two
is the mandibular notch.
On the medial aspect of the ramus is the mandibular foramen for the infe-
rior alveolar branch of the mandibular division of the trigeminal nerve,
which traverses the body within the mandibular canal, then emerges as the
mental nerve through the mental foramen on the lateral surface of the body
below and between the two premolars. The nerve supply to the incisors and
canine runs forward within the mandible beyond this point in the incisive
canal.
The upper border of the body bears the alveolar border with sixteen
dental sockets or alveoli.

Development

The mandible develops as membrane bone in the fibrous sheath of Meckel’s