NASAL CAVITIES 317 



inferior conchae. It divides into an ascending and descending 

 branch. Both run forwards ; the former on the middle 

 concha, the latter on the inferior concha. The lower of the 

 two inferior nasal nerves appears through a foramen in the 

 perpendicular part of the palate bone, immediately posterior 

 to the inferior concha, upon which it is distributed. 



The anterior ethmoidal nerve (O.T. nasal] should be ex- 

 posed as it descends in the groove upon the deep surface of 

 the nasal bone (p. 252). It gives medial branches to the 

 septum, and lateral branches to the muco-periosteum over the 

 anterior part of the lateral wall, and to the anterior parts of 

 the middle and inferior conchse. 



The main artery of supply to the nasal muco-periosteum 

 is the spheno-palatine, a branch of the internal maxillary. It 

 gains entrance to the nasal cavity through the spheno-palatine 

 foramen, in company with the posterior superior nasal nerves. 

 Its septal branch accompanies the naso-palatine nerve, whilst 

 others are distributed upon the lateral wall of the cavity. 

 Several twigs are given also by the descending palatine branch 

 of the internal maxillary and the two ethmoidal arteries, but 

 these are small and will be seen only in cases where the 

 injection of the subject has been unusually successful. 



SPHENO-PALATINE GANGLION AND INTERNAL 

 MAXILLARY ARTERY. 



The spheno-palatine ganglion is situated in the pterygo- 

 palatine fossa, on the lateral side of the spheno-palatine fora- 

 men ; and at this stage it can be exposed best by a dissection 

 from the medial or nasal side. 



Dissection. The muco-periosteum has already been re- 

 moved from the posterior part of the lateral wall of the nasal 

 cavity, and the inferior nasal branches of the anterior palatine 

 nerve have been found piercing the perpendicular part of the 

 palate bone. The dissector cannot fail to notice the course 

 taken by the trunk from which those filaments arise. The 

 lamina of bone which forms the medial wall of the pterygo- 

 palatine canal is so thin that the nerve can be distinctly seen 

 through it. By carefully opening up the canal with a small 

 chisel, and following the anterior palatine nerve upwards, the 

 dissector will be led to the ganglion in the pterygo-palatine 

 fossa. The naso-palatine nerve should at the same time be 

 traced to its origin. The ganglion is so hemmed in by the bony 

 walls of the fossa that it is very difficult to display it thoroughly ; 



