THE SKULL AS A WHOLE 169 



(protuberantia occipitalis externa), an important median point of 

 attachment for the occipital muscles and the dorsal ligament of 

 the neck. 



The ventral wall of the cranial portion is the basal part (basi- 

 cranium) of the entire skull. Its axial line, the basicranial axis, 

 continues, in general, that of the bodies of the vertebrae, and its 

 posterior portion is equivalent, morphologically, to vertebral seg- 

 ments. It is formed by a linear series of three bones, namely, 

 from back to front, the basilar portion of the occipital, the body 

 of the posterior sphenoid, and that of the anterior sphenoid (re- 

 spectively basioccipital, basisphenoid, and presphenoid bones). 

 Its extremely narrow, anterior portion forms the roof of a deep 

 groove which encloses the nasal portion of the pharynx. As view^ed 

 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 

 downward 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 w^hich serve for the attachment of the 

 external and internal pterygoid muscles of the mandible. 



The lateral wall of the cranial portion of the skull forms anteri- 

 orly a large part of the boundary of the orbit. The components 

 which do this are 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 posterior 

 sphenoid, or alisphenoid, and two membrane elements, the frontal 

 bone of the roof of the skull and the squamosal bone. The latter 

 is distinguishable as the support of the posterior root of the zygo- 

 matic arch, which projects outward and then downward immedi- 

 ately behind the orbit. This root is formed by a zygomatic process 

 (processus zygomaticus) of the squamosal bone, the tip of which 

 process forms a vertical plate, 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 



