central wedge that articulates with all other cranial bones. It is
a challenging bone to study because of its complex shape. As
, it consists of a central body and three
pairs of processes: the greater wings, lesser wings, and pterygoid
ĭ-goid). Within the
of the sphenoid are the
(see Figures 7.5c and d, and 7.14).
Te superior surface of the body bears a saddle-shaped prom-
sĭ-kah), meaning “±urk’s
saddle.” Te seat of this saddle, called the
forms a snug enclosure for the pituitary gland (hypophysis).
project laterally from the sphenoid body,
forming parts of (1) the middle cranial fossa (Figures 7.7 and
7.2b), (2) the posterior walls of the orbits (Figure 7.4a), and
(3) the external wall of the skull, where they are seen as ﬂag-
shaped, bony areas medial to the zygomatic arch (Figure 7.5).
form part of the ﬂoor of the anterior
cranial fossa (Figure 7.7) and part of the medial walls of the or-
bits. Te trough-shaped
Te mastoid process is full of air cavities (sinuses) called
toid air cells
. Teir position adjacent to the middle ear cavity
(a high-risk area for infections spreading from the throat) puts
them at risk for infection themselves. A mastoid sinus infec-
, is notoriously diﬃcult to treat. Because the
mastoid air cells are separated from the brain by only a very
thin bony plate, mastoid infections may spread to the brain as
well. Surgical removal of the mastoid process was once the best
way to prevent life-threatening brain inﬂammations in people
susceptible to repeated bouts of mastoiditis. ±oday, antibiotic
therapy is the treatment of choice.
the width of the middle cranial fossa (Figure 7.7). Te sphenoid
is considered the keystone of the cranium because it forms a
Body of sphenoid
(a) Superior view
Body of sphenoid
(b) Posterior view
The sphenoid bone.
(For related images, see
A Brief Atlas of the Human Body
Figures 5 and 9).