184 THE SKELETON. 



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

 terior 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 squa- 

 mous portion of the temporal bone ; its surface is convex arid rough for the 

 attachment of muscles, and presents, from behind forwards, the mastoid fora- 

 men, 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 Zygomalic 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; above, by the ptery- 

 goid ridge on the outer surface of the great wing of the sphenoid and squarnous 

 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-rnaxillary. 



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; internally, it joins at right 

 angles with the pterygo-maxillary fissure. This fissure opens a communica- 

 tion from the orbit into three fossae, the temporal, zygomatic, and spheno- 

 maxillary; it transmits the superior maxillary nerve, infraorbital artery, and 

 ascending branches from Meckel's ganglion. 



The ptery go-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 zygo- 

 matic, and transmits branches of the internal maxillary artery. 



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 ptery- 

 goid 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 

 foramina. Of these there are three on the posterior wall ; the foramen rotun- 

 dum above; below, and internal to this, the Vidian, and still more inferior and 

 internal, the pterygo-palatine. On the inner wall is the spheno-palatine fora- 

 men by which the spheno-maxillary communicates with the nasal fossa, and 

 below is the superior orifice of the posterior palatine canal, besides occasionally 

 the orifices of two or three accessory posterior palatine canals. 



ANTEEIOB KEGION 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 

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

 nasal eminences and margins of the orbit ; below, by the prominence of the 

 chin; on each side, by the malar bone, and anterior margin of the ramus of the 

 jaw. In the median line are seen from above downwards, the nasal eminences, 



