HEAD AND NECK OF THE HORSE 



147 



is included in a fold of mucous membrane, the plica alaris, that runs to 

 the lateral wing of the nostril. 



Dissection. — The constitution of the septum (septum nasi) between 

 the two nasal cavities should be determined by stripping the mucous 

 membrane from the surface at present exposed. A part of the septum — 

 the bony septum — is formed by the perpendicular plate of the ethmoid 

 and the vomer. The rest is cartilaginous, and formed by the cartilage 

 above described. 



By the exercise of a reasonable amount of care, the septum may be 

 removed bit by bit in such a manner that the mucous membrane clothing 

 its other side is left intact. This permits the dissector to examine the 

 blood vessels and nerves of the partition. 



Concho-frontal sinus. 



Ethmoidal vessels and nerve. 



Pharynx. I 



Soft palate. i I ^ 



N. nasalis posterior.' ' N. olfactorius to vomero-nasal organ. Hard palate. 



A. sphenopalatina (septal branch). 



Fig. 62. — Vessels and nerves of the nasal septum. 



In common with that of the nasal cavity in general, the mucous 

 membrane covering the septum is richly supplied with both blood 

 vessels and nerves. The vessels are derived from the ethmoidal branch 

 of the ophthalmic artery, which ramifies over the upper part of the 

 septum, and the nasal branch of the sphenopalatine artery, which 

 supplies the lower region. The veins begin in very rich plexuses that 

 are remarkably thick in some regions. 



The nerves are derived from two sources : — (1) The olfactory nerves 

 are distributed over the posterior dorsal part of the septum (and also 

 supply the vomero-nasal organ). (2) The trigeminal nerve contributes 

 branches from both its ophthalmic and its maxillary divisions. The 

 ethmoidal branch of the ophthalmic nerve terminates over the dorsal 

 part of the septum, and the nasal branch of the sphenopalatine nerve 

 supplies the lower part. 



Dissection. — With a pair of scissors, cut along the upper border of 



A. nasolabialis. 



