THE SKULL AS A WHOLE. 137 
A considerable portion of the anterior and dorsal wall of the 
orbit is formed by the facial complex. Dorsally, the roofing 
element of this region, the frontal bone, bears a curved lateral 
projection, the supraorbital process (processus supraorbitalis), 
which overhangs the orbit. Its narrower base expands into anterior 
and posterior tips, which lie parallel to the adjacent portion of the 
skull, and enclose with the latter corresponding anterior and 
posterior supraorbital incisures. The latter are converted: 
by ligament into foramina. The anterior wall of the orbit is formed 
in part by a loosely articulated element, the lacrimal bone, the 
lateral margin of which projects from the orbital rim as a blunt 
subcutaneous process (processus subcutaneus). On the ventral 
side of its base is the orbital opening of the nasolacrimal canal 
(canalis nasolacrimalis), the bony enclosure of the nasolacrimal 
duct, which in the natural condition leads from the corneal surface 
of the eye to the anterior portion of the nasal fossa. A smaller 
projection forming the ventral boundary of the nasolacrimal 
aperture is the hamulus lacrimalis. Finally, in the ventral 
anterior angle of the orbit, the bases of the three posterior cheek- 
teeth encroach to a considerable extent on the orbital space. They 
are separated from the orbital wall by a deep infraorbital groove 
(sulcus infraorbitalis), which leads forward into the canal of the 
same name. They partly conceal two important apertures of this 
region, the orbital opening of the pterygopalatine canal (canalis 
pterygopalatinus), leading to the palatal surface, and the spheno- 
palatine foramen (foramen sphenopalatinum), leading to the 
nasal fossa. The pterygopalatine canal opens ventrally in the 
palato-maxillary suture of the hard palate by a rounded aperture, 
the greater palatine foramen (foramen palatinum majus). 
The nasal cavity (cavum nasi) is enclosed by the maxilla and 
premaxilla, with the assistance of paired roofing elements, the 
nasal bones. Apart from the incisive foramina, which are closed 
in the natural condition, the cavity is open at two points. Poste- 
riorly it communicates with the ventral surface of the skull by the 
choanae, which, in the rabbit, are incompletely divided. An- 
teriorly it opens to the outside by the piriform aperture (apertura 
piriformis). The cavity is divided into right and left portions, 
the nasal fossae. In the divided skull it is seen thac the division 
is effected chiefly through a median vertical, cartilaginous plate, 
