_I_, Roof of cranium; _II_, base of cranium; _III_, posterior wall of
cranium; _IV_, anterior wall of cranium; _A_, anterior cranial
fossa; _B_, middle cranial fossa; _C_, posterior cranial fossa; _a_,
body of presphenoid; _a′_, body of postsphenoid; _c_, palate bone;
_d_, vomer; _e_, occipital; _f_, occipital condyle; _g_, sagittal
crest; _h_, frontal sinus; _h′_, cranial plate of frontal bone; _i_,
cribriform plate of ethmoid bone; _i′_, ethmoidal foramen; _k_,
ethmoturbinals; _l_, parietal bone; _l′_, _l″_, squamous temporal
bone; _l‴_, temporal wing of sphenoid bone; _m_, sella turcica;
_m′_, dorsum sellæ; _n_, optic foramen; _o_, foramen lacerum
orbitale; _p_, foramen rotundum; _q_, foramen ovale; _r_, _r′_,
carotid foramina; _s_, tentorium osseum; _t_, foramen lacerum; _u_,
_u′_, orifices of parieto-temporal canal; _v_, condyloid canal; _w_,
canal for trigeminal nerve; _x_, internal auditory meatus; _y_,
_y′_, orifices of canal for inferior occipital sinus; _z_, floccular
fossa. (After Ellenberger, in Leisering’s Atlas.)
]
The body of the =sphenoid bone= is flattened dorso-ventrally. The sella
turcica is shallow, but the dorsum sellæ is well developed and bears
=posterior clinoid processes=. A pair of =anterior clinoid processes=
project back from the roots of the orbital wings. The latter are
relatively small and are crossed externally by a crest, which is
continued forward upon the palate bone. The temporal wings are extensive
and articulate above with the parietals. Perforating the roots of the
wings are the following foramina, named from before backward: The optic
passes through the orbital wing. The foramen lacerum orbitale is a
little lower and is at the junction of the wings. The foramen rotundum
opens into the alar canal, which passes through the root of the short
but wide pterygoid process. The foramen ovale is near the posterior
border of the temporal wing. There is no sphenoidal sinus.
The =ethmoid bone= is highly developed. The cribriform plate is
extensive, and the olfactory fossæ are very deep. The crista galli is
little developed, and often incomplete. The perpendicular plate is long.
The lateral masses are greatly developed and bulge upward into the
frontal sinus. There are four large endoturbinals and six ectoturbinals.
The lamina papyracea is extensive and forms the inner wall of the
maxillary sinus. Its lower border joins the palatine process of the
maxilla and the horizontal part of the palate bone. A shelf-like plate
extends inward from its lower part and concurs with the similarly
incurved part of the palate bone in forming the =transverse lamina=
(Lamina transversalis), which divides the olfactory fundus of the nasal
cavity from the naso-pharyngeal meatus.