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 zygomatic 

 arch. The dorsal boundary of the fossa is formed by a pronounced 



