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.
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.
7. The =Posterior nares=. These form a median unpaired opening (fig. 43, A, 5) bounded by the pterygoids.
8. The =Posterior palatine vacuities=. Each is bounded by the maxillae in front, the maxillae and transpalatine externally, the transpalatine and pterygoid behind, and the palatine on the inner side (fig. 43, A, 7).
9. The =Anterior palatine vacuity=. This is unpaired and is bounded by the premaxillae (fig. 43, A, 8).
The mandible is a strong compact bony structure formed of two halves or =rami=, which are suturally united at the symphysis in the middle line in front. Each ramus is formed of six separate bones.
The most anterior and largest of these is the _dentary_ (figs. 44, 20, and 45, 18), which forms the symphysis, and greater part of the anterior half of the jaw, and bears along the outer part of its dorsal border a number of sockets or =alveoli= in which the teeth are placed. Lying along the inner side of the dentary is a large splint-like bone, the _splenial_ (fig. 45, 19), which does not extend so far forwards as the symphysis, and is separated from the dentary posteriorly by a large cavity. Forming the lower part of all the posterior half of the jaw is the large _angular_ (figs. 44, 22, and 45, 20), which underlies the posterior part of the dentary in front and sends a long process below that bone to the splenial. On the inner side of the jaw there is an oval vacuity, the =internal mandibular foramen= (fig. 45, 28), between the angular and the splenial; through this pass blood-vessels and branches of the inferior dental nerve. Lying dorsal to the angular is another large bone, the _supra-angular_ (figs. 44, 18, and 45, 21). It extends back as far as the posterior end of the jaw and forwards for some distance dorsal to the dentary and splenial. It forms part of the posterior margin of a large vacuity, the =external mandibular foramen=, which is bordered above and in front by the dentary and below by the angular; it gives passage to the cutaneous branch of the inferior dental nerve. The concave surface for articulation with the mandible and much of the posterior end of the jaw is formed by a short but solid bone, the =articular= (fig. 45, 22), which in young skulls rather readily becomes detached. The remaining mandibular bone is the _coronoid_ (fig. 45, 23), a very small bone of irregular shape attached to the angular below, and to the supra-angular and splenial above.