Four foramina leading into the cranial cavity are visible in a lateral view of the skull, craniad of the tympanic bulla. The one nearest the bulla is the =foramen ovale= (_u_) for the third division of the fifth nerve; next craniad of this is the =foramen rotundum= (_v_) for the second division of the fifth nerve. These two foramina pierce the alisphenoid: just craniad of them, between the alisphenoid and the orbitosphenoid, is the large =orbital fissure= (_r_) (foramen lacerum anterius), which transmits the third, fourth, and sixth cranial nerves and the first division of the fifth. Dorsocraniad of the orbital fissure is the =optic foramen= (_w_), for the =optic nerve=.
Ventrad of the cranial portion of the orbit is the large =sphenopalatine foramen= (_q_), for the nerves and arteries of the same name. Just craniad of this is the small caudal opening of the =posterior palatine canal=, which passes through the substance of the palatine bone and opens on its ventral surface near its cranial margin. Just dorsad of the cranial root of the zygomatic arch is the opening of the =lachrymal canal= (_x_), while the root of the arch is pierced by the large =infraorbital foramen= (_y_), which transmits the =infraorbital= nerves and artery from the orbit.
The teeth (13-18), implanted along the alveolar border of the maxillary and premaxillary, form a prominent feature in a lateral view: they are described in the account of the alimentary canal.
The =ventral surface= of the skull (Fig. 41) is very complex. It is separated by the orbits into a caudal and a cranial portion, united by a narrow median trough-like part. Laterad of this trough-like part are visible parts of the orbit and the zygomatic arches, which do not properly belong to the ventral surface and have already been described.
[Illustration: FIG. 41.--SKULL, VENTRAL VIEW.
1, occipital bone; 2, temporal; 3, sphenoid; 4, presphenoid; 5, frontal; 6, malar; 7, vomer; 8, palatine; 9, maxillary; 10, premaxillary. _a_, foramen magnum; _b_, occipital condyles; _c_, jugular process; _d_, tympanic bulla; _e_, mastoid process; _f_, stylomastoid foramen; _g_, external auditory meatus; _h_, jugular foramen; _i_, styliform process; _j_, groove for Eustachian tube; _k_, foramen ovale; _l_, foramen rotundum; _m_, pterygoid process of sphenoid; _n_, perpendicular plate of palatine; _o_, choanæ or posterior nares; _p_, zygomatic arch; _q_, cranial end of posterior palatine canal; _r_, palatine grooves; _s_, foramina incisiva or anterior palatine foramina; _t_, opening of pterygoid canal.]