THE SPHENO-MAXILLARY FOSSA. 



227 



the canal in the ethmoid, known as the infmidibulum. In the former cases one of 

 the cells of the ethmoid is particularly liable to make a projection — i\\Q frontal bulla 

 — into the floor of the sinus. 



The antrum (Fig. 255) is a four-sided pyramid with an irregular base towards 

 the nasal cavity (Merkelj. The apex is at the malar. In addition to the base, 

 an orbital, an anterior, and a posterior surface are recognized. Owing to the 

 irregularity of the base there is a groove instead of an angle below, above the 

 alveolar process. (This relation is described with the upper jaw.) The large in- 

 ternal aperture in the superior maxilla is divided into two when the other bones are 

 in place. Both are near the top ; the anterior opens into the infundibulum, the pos- 

 terior into the middle meatus. Partial septa project into the antral cavity. An 

 important projection is that of the infra-orbital canal. 



The zygomatic fossa (Fig. 258) is the space internal to the lower jaw, sepa- 

 rated from the temporal fossa by an imaginary plane at the level of the upper 

 border of the zygoma. It is open below and behind. The front wall is made by 



Orbital surface of great 

 wing of sphenoid 



Frontal process of malar 



Cut surface of zygoma 



Tympanic plate of 

 temporal W, 



Mastoid process 



Optic foramen 

 Sphenoidal fissure 

 Sphenoidal sinus 

 Foramen rotundum 



Vidian canal 



Probe in pterygo-palatine 

 canal 

 Posterior wall of spheno- 

 maxillary fossa 



Palate bone 



-Hamular process of internal pterygoid plate 

 Zygomatic surface of external pterygoid plate 



Portion of right half of skull, showing posterior wall of spheno-maxillary fossa. The superior maxilla, ethmoid, 



and part of malar have been removed. 



the maxilla, what little roof there is by that part of the great wing of the sphenoid 

 internal to the infratemporal crest, and the inner wall by the external pterygoid 

 plate. It has two important fissures, — the spheno-maxillary, horizontal, admitting 

 to the orbit, between the sphenoid and maxilla ; the other, the pterygo-maxil- 

 lary, vertical, between the maxillary bone and the front of the united pterygoid 

 plates. 



The spheno-maxillary fossa (Fig. 259) is a small cavity below and behind 

 the apex of the orbit at the point of junction of the spheno-maxillary and the 

 pterygo-maxillary fissures. The posterior wall is formed by the sphenoid above the 

 roots "of the pterygoid plates. The transverse and antero-posterior diameters of the 

 fossa are about fifteen millimetres. It contains the spheno-palatine or Meckel's 

 ganglion. The foramen rohmd^im. opens into it behind, transmitting the superior 

 maxillary division of the trifacial nerve. More internal and lower on the posterior 

 wall is the orifice of the Vidian canal, transmitting the great superficial and deep 

 petrosal nerves and accompanying blood-vessels. Still nearer the median line is 



