106 OSTEOLOGY. 



The Mastoid Portion is bounded in front by the anterior root 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 portion of the temporal bone ; 

 its surface is convex and rough for the attachment of muscles, and presents, from 

 behind forwards, the mastoid foramen, the mastoid process, the external auditory 

 meatus, surrounded by the auditory process, and, most anteriorly, the glenoid 

 fossa, bounded in front by the eminentia articularis, behind by the vaginal process. 



THE ZYGOMATIC FOSSAE. 



The Zygomatic fossa is an irregular-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 ; above, by the pterygoid ridge 

 on the outer surface of the great wing of the sphenoid and 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 jaw. It contains the lower part of the Temporal, the External and 

 Internal pterygoid muscles, the internal maxillary artery, the 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 maxillary and a small part of the palate bone ; 

 externally, by a small part of the malar bone ; 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, infra-orbital artery, and ascending branches from 

 Meckel's ganglion. 



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

 the inner extremity of the preceding ; it is an elongated 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, 

 and transmits branches of the internal maxillary artery. 



THE SPHENO-MAXILLABY 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; in front, by the superior maxillary bone; behind, by the 

 pterygoid process 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 fora- 

 mina. Of these there are three on the posterior wall, the foramen rotundum 

 above, the Vidian below and internal, and, still more inferior and internal, the 

 pterygo-palatine. On the inner wall is the spheno-palatine foramen by which it 

 communicates with the nasal fossa, and below, the superior orifice of the posterior 

 palatine canal, besides occasionally the orifices of two or three accessory posterior 

 palatine canals. 



ANTERIOR EEGION OF THE SKULL. 



The Anterior Eegion of the Skull, which forms the face, is of an oval form, 

 presents an irregular surface, and is excavated for the reception of the two prin- 

 cipal organs of sense, the eye and the nose. It is bounded above by the nasal 



