302 HEAD AND NECK 



cavernous sinus, to the foramen rotundum, through which it 

 enters the pterygo-palatine fossa. It crosses the upper part 

 of that fossa, curves laterally through the pterygo-maxillary 

 fissure into the infra-temporal fossa, and, near the middle 

 of the inferior orbital fissure, enters the infra-orbital canal, 

 where it receives the name of infra-orbital. The infra - 

 orbital canal traverses the floor of the orbit, which, it should 

 be remembered, forms the roof of the maxillary sinus 

 also. Finally, leaving the infra-orbital canal, the nerve 

 emerges upon the face through the infra-orbital foramen, and 

 breaks up, under cover of the quadratus labii superioris, 

 into numerous branches which unite with twigs from the 

 facial nerve to form a dense plexus. Its terminal filaments 

 are distributed to the lower eyelid, the nose, and the upper 

 lip. The course of the maxillary nerve may be separated 

 into five stages, in each of which branches are given off. 

 These are : 



1. Within the cranium, . Meningeal (p. 238). 



2. In the pterygo-pala- ^ _ , 



tine fossa, . . / Spheno-palatme. 



3. In the infra-temporal fZygomatic (already described, p. 261). 



fossa, . . . \ Posterior superior alveolar. 



4. In the infra-orbital /Middle superior alveolar. 



canal, . . . \Anterior superior alveolar. 

 ( Palpebral, ^ 



5. In the face, . . \ Nasal, J- already described : (p. 15). 



{ Labial, J 



The spheno-palatine branches are two stout twigs which arise 

 from the inferior 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. 



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. 



Nervi Alveolares Superiores. There are usually three 

 superior alveolar nerves which are distinguished as posterior, 

 middle, and anterior. The middle superior alveolar nerve is 

 sometimes absent as a separate trunk, in which case its fibres 

 arise 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 



