3 88 HEAD AND NECK 



The zygomatic nerve, which has already been dissected 

 in the orbit, can now be traced to its origin from the 

 maxillary nerve in the infra-temporal fossa. The spheno- 

 palatine branches are two stout twigs which arise from the 

 under aspect of the maxillary nerve, and proceed vertically 

 downwards, in the pterygo-palatine fossa, to the spheno-palatine 

 ganglion, of which they constitute the sensory roots. 



Nervi Alveolares Superiores. These are usually three in 

 number, and are distinguished as posterior, middle, and 

 anterior. The middle superior alveolar nerve is sometimes 

 absent as a separate trunk, in which case it arises in common 

 with the anterior superior alveolar branch. 



The posterior superior alveolar nerve takes origin in the 

 infra-temporal fossa, and almost immediately divides into 

 two branches, which proceed downwards upon the posterior 

 aspect of the body of the maxilla. They contribute a few 

 fine filaments to the mucous membrane of the cheek and 

 to the gum, and then disappear into the minute posterior 

 dental foramina to supply the three molar teeth and the lining 

 membrane of the maxillary sinus. 



The middle superior alveolar nerve supplies the two 

 premolar teeth. It arises from the infra-orbital nerve, and 

 can be easily detected (when present) by gently raising the 

 parent trunk from the floor of the infra-orbital canal. It 

 descends in a minute canal which traverses the lateral wall 

 of the maxillary sinus. 



The anterior superior alveolar nerve, much the largest of 

 the three alveolar branches, springs from the infra-orbital as it 

 approaches the anterior part of the canal. It can be brought 

 into view by raising the parent trunk from the floor of the 

 canal, and it will then be seen to enter a special bony tunnel 

 which traverses the maxilla in the anterior wall of the 

 maxillary sinus. The dissector should endeavour to open 

 up this canal with the chisel. After supplying a branch to 

 the mucous membrane of the lower and anterior part of 

 the nasal cavity, the anterior superior alveolar nerve divides 

 into branches for the incisor and the canine teeth. 



While traversing the maxilla, the three superior alveolar branches 

 communicate with each other, and form two nerve-loops (Fig. 152). 

 Numerous twigs proceed from these, and join in a fine plexus. It is from 

 this plexus that the terminal filaments to the teeth and gum take origin. 



Arteria Infra - orbitalis. The infra -orbital artery is a 



