THE SKULL AS A WHOLE 67 



fossa. Running at right angles to the fissure is the spheno- 

 maxillary fissure opening into the orbit. 



The sphenomaxUlary fossa is a small triangular space at 

 the angle of junction of the above-named fissures, placed 

 beneath the apex of the orbit. It is bounded above by the 

 body of the sphenoid, in front by the superior maxilla, behind 

 by the base of the pterygoid, and internally by the vertical 

 plate of the palate. It has three fissures terminating in it 

 the sphenoidal, sphenomaxillary, and pterygomaxillary. It 

 communicates with four fossae the orbital, nasal, zygomatic, 

 and middle fossa of the base of the skull; and has opening into 

 it five foramina three from behind, the foramen rotundum, 

 the Vidian, and the pterygopalatine canals; internally is the 

 sphenopalatine foramen, and inferiorly the posterior palatine 

 canals, and occasionally the accessory posterior palatine canals. 



The external base of the skull ("base of skull" properly 

 means base of the cranium, and does not include the facial 

 bones; the usual description, however, will be followed, and 

 the inferior maxilla included) is divisible into three parts- 

 anterior, middle, and posterior. The anterior division consists 

 of the palate, alveolar arches, and body of the inferior maxilla. 

 It is traversed longitudinally by a median suture, and trans- 

 versely by that between the maxillary and palate bones. In 

 front is the anterior palatine fossa, with the four foramina 

 opening into it; farther back are the under surface of the 

 tuberosity of the palate, the apertures of the posterior and 

 external palatine canals, and the posterior nasal spine. 



The middle division extends back to the foramen magnum, 

 and is called the guttural fossae (relating to the throat). In 

 the midline is the basilar process, and in front of that the 

 body of the sphenoid covered by the alse of the vomer. On 

 each side the petrous portion reaches to the extremity of the 

 basilar process, and between the petrous and squamous is 

 the back part of the great wing of the sphenoid. In front 

 are the posterior nares, or choanoe (funnels), separated by the 

 vomer, bounded above by the sphenoid, below by the hori- 

 zontal plates of the palate bones, and laterally by the internal 

 pterygoid plates. On each side are the pterygopalatine and 

 Vidian canals, the scaphoid and pterygoid fossae. A line from 

 the external pterygoid plate to the spine of the sphenoid sepa- 

 rates this surface from the zygomatic fossa; internal to this 



