3 i6 HEAD AND NECK 



The olfactory nerves are from twelve to twenty in number. 

 They are formed by numerous fine nerve filaments, which 

 spring from the olfactory cells of the olfactory mucous mem- 

 brane, and they are arranged in two groups ; a medial or septal 

 group, from the upper part of the septum (p. 307), and a lateral 

 group, from the upper third of the lateral wall of the nasal 

 cavity. The nerve filaments lie in the muco-periosteum, but 

 the nerves which they form are lodged in shallow bony 

 grooves and small bony canals in the walls of the nasal cavity. 

 At the roof of the nose the nerves pass through the foramina 

 in the cribriform plate of the ethmoid ; then they pierce the 

 meninges, from which they derive sheaths, and they end in 

 the lower part of the olfactory bulb of the same side. 



Dissection. Follow the naso-palatine nerve, which was 

 exposed on the nasal septum, across the roof of the nasal cavity 

 to the spheno-palatine foramen in the lateral wall of the nose. 

 By dissecting carefully in the muco-periosteum in the neigh- 

 bourhood of the foramen, in a good part, the dissector may be 

 able to display one or more of the posterior superior nasal nerves. 

 At the same time he should display the spheno-palatine branch 

 of the internal maxillary artery which enters the nose through 

 the spheno-palatine foramen. 



The posterior superior nasal nerves arise from the spheno- 

 palatine ganglion and from the nerve of the pterygoid canal. 

 In spite of the fact that they are minute filaments, the 

 dissector should endeavour to trace them to their distribution 

 upon the lateral wall. They enter the nose through the 

 spheno-palatine foramen, which is situated at the posterior 

 end of the superior meatus ; and are distributed to the muco- 

 periosteum over the upper and middle conchae, and the 

 posterior part of the septum. 



Dissection. Make a vertical incision through the muco- 

 periosteum over the posterior part of the medial pterygoid 

 lamina, then carefully raise the membrane, reflect it forwards 

 and seek for the inferior nasal nerves. They both pierce the 

 perpendicular plate of the palate bone ; the upper one at a 

 point on a level with the interval between the posterior ends of 

 the middle and inferior conchae, and the lower at the level of 

 the posterior end of the inferior concha. 



The inferior nasal nerves are two in number ; they both 

 arise from the anterior palatine nerve. 



The upper of the two inferior nasal nerves emerges through 

 a small aperture in the perpendicular part of the palate bone, 

 at a point between the posterior extremities of the middle and 



