216 THE SKELETON. 



external angular process of the frontal bone and about one and a half inches behind 

 it. This fossa is deeply concave in front, convex behind, traversed by grooves which 

 lodge branches of the deep temporal arteries, and filled by the Temporal muscles. 



The Mastoid Portion. 



The Mastoid Portion of the side of the skull is bounded in front by the tubercle 

 of the zygoma ; above, by a line which runs from the posterior root of the zygoma 

 to the end of the masto-parietal suture ; behind and below by the masto-occipital 

 suture. It is formed by the mastoid and part of the squamous and petrous por- 

 tions of the temporal bone ; its surface is convex and rough for the attachment of 

 muscles, and presents, from behind forward, the mastoid foramen, the mastoid 

 process, the external auditory mea^us surrounded by the auditory process, and, 

 most anteriorly, the temporo-maxillary articulation. 



The Zygomatic Fossa. 



The Zygomatic Fossa is an irregularly shaped cavity, situated below and on the 

 inner side of the zygoma ; bounded, in front, by the tuberosity of the superior 

 maxillary bone and the ridge which descends from its malar process ; behind, by 

 the posterior border of the pterygoid process and the eminentia artlcularis ; above, 

 by the pterygoid ridge on the outer surface of the great wing of the sphenoid and 

 the under part of the squamous portion of the temporal ; below, by the alveolar 

 border of the superior maxilla ; internally, by the external pterygoid plate ; and 

 externally, by the zygomatic arch and ramus of the lower jaw. It contains the 

 lower part of the Temporal, the External and Internal pterygoid muscles, the 

 internal maxillary artery, and inferior maxillary nerve and their branches. At its 

 upper and inner part may be observed two fissures, the spheno-maxillary and 

 pterygo-maxillary. 



The Spheno-maxillary Fissure, horizontal in direction, opens into the outer and 

 back part of the orbit. It is formed above by the lower border of the orbital surface 

 of the great wing of the sphenoid; below, by the external border of the orbital 

 surface of the superior maxilla and a small part of the palate bone ; externally, by 

 a small part of the malar bone: 1 internally, it joins at right angles with the 

 pterygo-maxillary fissure. This fissure opens a communication from the orbit into 

 three fossae the temporal, zygomatic, and spheno-maxillary ; it transmits the 

 superior maxillary nerve and its orbital branch, the infraorbital vessels, and 

 ascending branches from the spheno-palatine or Meckel's ganglion. 



The Pterygo-maxillary Fissure is vertical, and descends at right angles from 

 the inner extremity of the preceding ; it is a V-shaped interval, formed by 

 the divergence of the superior maxillary bone from the pterygoid process of the 

 sphenoid. It serves to connect the spheno-maxillary fossa with the zygomatic fossa, 

 and transmits branches of the internal maxillary artery. It forms the entrance from 

 the zygomatic fossa to the spheno-maxillary fossa. 



The Spheno-maxillary Fossa. 



The Spheno-maxillary Fossa is a small, triangular space situated at the angle of 

 junction of the spheno-maxillary and pterygo-maxillary fissures, and placed beneath 

 the apex of the orbit. It is formed above by the under surface of the body of 

 the sphenoid and by the orbital process of the palate bone ; in front, by the superior 

 maxillary bone ; behind, by the anterior surface of the base of the pterygoid 

 process and lower part of the anterior surface of the great wing of the sphenoid ; 

 internally, by the vertical plate of the palate. This fossa has three fissures 

 terminating in it the sphenoidal, spheno-maxillary, and pterygo-maxillary ; it 

 communicates with three fossae, the orbital, nasal, and zygomatic, and with the 

 cavity of the cranium, and has opening into it five foramina. Of these, there are 



1 Occasionally the superior maxillary bone and the sphenoid articulate with each other at the 

 anterior extremity of this fissure ; the malar is then excluded from entering into its formation. 



