130 ANATOMY OF THE RABBIT. 
segments. It is formed by a linear series of three bones, namely, 
the basilar portion of the occipital, the body of the posterior 
sphenoid, and that of the anterior sphenoid (respectively basi- 
occipital, basisphenoid and presphenoid bones). Its ex- 
tremely narrow, anterior portion forms the roof of a deep groove 
which encloses the nasal portion of the pharynx. As viewed from 
the ventral surface, it is seen to disappear in the facial complex at 
some distance dorsal to the posterior margin of the bony palatine 
bridge. Laterally, it is separated from the orbit on either side by a 
vertical plate formed by the palatine bone, and also by two down- 
ward projections of the posterior sphenoid, the medial and lateral 
laminae of the pterygoid process (processus pterygoideus). 
These structures enclose between them the pterygoid fossa (fossa 
pterygoidea), the walls of which serve for the attachment of the 
external and internal pterygoid muscles of the mandible. 
The lateral wall of the cranial portion forms anteriorly a large 
part of the boundary of the orbit. The cranial wall of the orbit is 
partly formed by two upward projections of the basicranium, 
namely, the lesser or orbital wing of the anterior sphenoid, or 
orbitosphenoid and the greater or temporal wing of the pos- 
terior sphenoid, or alisphenoid. The remaining portion is formed 
by membrane elements, including the frontal bone of the roof of 
the skull and the squamosal bone, the latter distinguishable as the 
support of the posterior root of the zygomatic arch. Immediately 
behind the orbit, the root of the zygomatic arch projects outward 
and then downward. It is formed by a zygomatic process (proces- 
sus zygomaticus) of the squamosal bone, and the tip of this forms 
a vertical plate, which is united by a horizontal suture with the 
zygomatic bone. On the ventral side of the process, close to the 
cranial wall, is the glenoid cavity or mandibular fossa (fossa 
mandibularis), for articulation with the mandible. On its dorsal 
side, but more especially on the adjacent portion of the cranial wall, 
there is a shallow, horizontal groove, lodging in the natural condi- 
tion the temporalis muscle of the mandible, and therefore represent- 
ing a greatly reduced temporal fossa (fossa temporalis). In the 
natural condition the anterior portion of the groove is converted 
into a foramen through the presence of a stout ligament extending 
from the posterior supraorbital process to the base of the zygomatie 
arch. The dorsal boundary of the fossa is formed by a pronounced 
