Dorsal surface.
1. The Supratemporal fossae. Each is bounded internally by the parietal, behind by the post-temporal bar formed by the parietal and squamosal, and externally by the supratemporal arcade formed by the squamosal and postfrontal. The postfrontal meets the parietal in front and forms the anterior boundary of the supratemporal fossa.
2. The Lateral temporal or infratemporal fossae. These lie below and to the outer side of the supratemporal fossae. Each is bounded dorso-internally by the supratemporal arcade; and behind by a continuation of the post-temporal bar formed by the quadrate and quadratojugal. The external boundary is the infratemporal arcade formed of the quadratojugal and jugal, while in front the fossa is separated from the orbit by the postorbital bar formed by the junction of outgrowths from the postfrontal and jugal.
3. The Orbits. Each is bounded behind by the postorbital bar, externally by the jugal forming a continuation of the infratemporal arcade, in front by the lachrymal, and internally by the frontal and prefrontal.
4. The Anterior nares. These form an unpaired opening bounded by the premaxillae.
Posterior surface.
5. The Foramen magnum. The exoccipitals form the chief part of its boundary, but part of the ventral boundary is formed by the basi-occipital.
6. The Pterygoid fossae. These form a pair of large cavities at the sides of the occipital region of the skull. The dorsal boundary is formed by the quadrate and quadratojugal, the ventral by the pterygoid, the internal chiefly by the quadrate, pterygoid, alisphenoid, and basisphenoid. The transpalatine forms a small part of the external boundary which is incomplete.
Ventral surface.
7. The Posterior nares. These form a median unpaired opening (fig. 43, A, 5) bounded by the pterygoids.