326 SPLANCHNOLOGY. 



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 

 surface moist, preserve its sensitiveness, and defend it from 

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



Longitudinal section of the head, showing the pharynx and nasal chamber— the septum nasi 

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

 nacal meatus ; /, Cavity of the pharynx ; g. Opening of Eustachian tube ; h, Isthmus faucium ; 

 i, Posterior naris ; k, Opening of the larynx ; I, Opening of the cesophagus. 



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 backward 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 

 inferior maxillary sinus, is generally isolated from the rest. 

 (See p. 44.) The sinuses are lined with mucous membrane, and 

 contain air. The laasal chambers give passage to the respired 



