BONES OF THE SKULL. 



meatus below and in front; a fissure (auricular) for Arnold's 

 nerve separates the plate from the mastoicj and squamous tem- 

 poral behind. The external auditory meatus curves inward and 

 slightly forward, with its convexity upward, to the tympanum. 

 Behind this the mastoid process, a large and nipple-like proc- 

 ess, projects downward; it usually presents a (mastoid) fora- 

 men, in the occipito-mastoid suture, for a vein. [156] 



Zygomatic Fossa. This is a deep hollow in front of the an- 

 terior root of the zygoma and below the infra-temporal crest 

 (pterygoid ridge). The postero-external (zygomatic) surface 

 of the superior maxilla forms the anterior wall, being limited 

 externally by the sharp lower border of its malar process, and 

 superiorly by the lower border of the spheno-maxillary fissure; 

 it presents foramina (posterior dental canals) leading to the 

 upper molars, and also a projection (tubercle) behind the last 

 molar. The external pterygoid plate of the sphenoid, which 

 forms the inner wall, is separated from the superior maxilla 

 above by a narrow and vertical cleft (pterygo-maxillary fissure), 

 and below by the tuberosity of the palate bone ; the posterior 

 border of the plate is thin and may have spiny points. [156] 



The under (zygomatic) surface of the great wing of the sphe- 

 noid overhangs the fossa, extending from the alar spine to the 

 spheno-maxillary fissure and outward to the pterygoid ridge: 

 it presents an oval hole (foramen ovale) just behind the root 

 of the pterygoid plate, and behind this a smaller orifice (fora- 

 men spinosum) close to the alar spine. Part of the roof is 

 formed by a small triangular area on the squamous temporal 

 between the articular eminence and anterior root of the zy- 

 goma. At the back of the fossa are the styloid and vaginal 

 processes of the sphenoid. Internally the fossa communicates 

 with the orbit and spheno-maxillary fossa, by the spheno- 

 maxillary and pterygo-maxillary fissures respectively; these 

 fissures join at right angles in an L. [157] 



Spheno-maxillary Fossa. This corresponds to the angular 

 interval between the spheno-maxillary and pterygo-maxillary 



[9] 



