_O_, Frontal sinus; _r_, sphenoidal sinus; _t_, cerebral compartment
of cranium; 1–3, ridges (juga) corresponding to fissures of lateral
surface of cerebrum; 4, groove for middle cerebral artery; 5,
entrance to for. lacerum orbitale; 6, entrance to optic foramen; 7,
8, grooves on sphenoid bone; 9, incisura spinosa; 9′, groove for
middle meningeal artery; 10, fossa for pyriform lobe of cerebrum;
11, incisura ovalis; 12, incisura carotica; 13, internal auditory
meatus; 14, foramen lacerum basis cranii; 15, hypoglossal foramen;
16, petrous temporal; 17, orifice of aquæductus vestibuli; 18,
orifice of aquæductus cochleæ; 19, foramen magnum; 20, petrosal
crest; 21, two plates of frontal bone; 22, supraoccipital; 23,
basioccipital; 24, tentorium osseum; 25, body of sphenoid. (After
Ellenberger-Baum, Top. Anat. d. Pferdes.)
]
The =posterior= or =nuchal surface= (Norma occipitalis) is formed by the
occipital bone. It is trapezoidal in outline, wider below than above,
concave dorso-ventrally, convex transversely. It is separated from the
superior surface by the =occipital crest=, and from the lateral surfaces
by the =superior curved lines= (Lineæ nuchæ superiores). Below the crest
are two rough areas for the attachment of the complexus muscles. A
little lower is a central eminence on the sides of which the ligamentum
nuchæ is attached. At the lowest part centrally is the =foramen magnum=,
at which the brain and spinal cord meet; this is bounded laterally by
the =occipital condyles=, which are flanked by the =paramastoid= or
=styloid processes= (Processus jugulares).
The =apex= of the skull is formed by the bodies of the premaxillæ and
mandible, carrying the incisor teeth.