326 SPLAXCHNOLOGY. 



The nasal chambers are lined by a delicate, pale rose-coloured 

 mucous membrane, the pituitary or Schneiderian membrane, 

 which is continuous with the skin at the nostrils, the mucous 

 membrane of the pharynx, and with that lining the sinuses of the 

 head ; and, in some animals, with the conjunctiva, by the lach- 

 rymal duct. It is attached, and sometimes inseparably, to the 

 perichondrium of the septum and the periosteum of the bones. 

 The pituitary membrane is sensitive, varying in vascularity and 

 thickness, being most vascular on the septum and turbinated 

 bones, and thinnest in the sinuses ; its free surface is smooth, 

 and covered by epithelium. Near the external opening the 

 epithelium is scaly, the remainder ciliated. It is studded with 

 numerous follicles or crypts, which secrete mucus to keep the 



FIG. 111. 



Longitudinal section of the Lead, showing the pharynx and nasal chamber the septum nasi being 

 removed, a, Superior turbinal ; b, Inferior turbiual ; c, Superior, d, Middle, and e, Inferior nasal 

 meatus ; /, Cavity of the pharynx ; g, Opening of Eustachiau tube ; h, Isthmus faucium ; i, Posterior 

 naris ; k, Opening of the larynx ; I, Opening of the oesophagus. 



surface moist, preserve its sensitiveness, and defend it from 

 noxious vapours. The blood-vessels come from the lateral nasal 

 and spheno-palatine arteries. The nerves are the first or olfac- 

 tory pair, or nerves of the special sense of smell, and certain 

 branches of the fifth. The canal of Jacobson in the horse is a 

 blind canal, with its orifice on the floor of the nasal chamber 

 about the incisive opening ; it runs backwards for about four 

 inches, being related with the septum nasi. Its use is unknown. 

 Each nasal chamber communicates with four distinct sinuses 

 Frontal, Maxillary, Ethmoid, and Sphenoid. The maxillary 

 sinus is divided into two ; the anterior cavity, often called the 



