SPECIAL ANATOMY. 141 



than tbe superior ; posteriorly it gradually disappears ; 

 anteriorly it presents a bifid cartilaginous prolongation, 

 one of the divisions of which runs to the inner, the other 

 to the outer wing of the nostril. It has also an anterior 

 and a posterior division ; the former helps to form the 

 middle meatus, the latter enters into the composition of 

 the inferior maxillary sinus. Thus the superior meatus, 

 the longest and narrowest, is between the roof of the 

 chamber and the upper surface of the superior turbinated 

 bone. It extends from the anteiior naris to the cribriform 

 plate. The middle meatus, between the ossa turbinata, 

 comprises the anterior cavities of both turbinated bones, 

 and extends from the anterior naris to the ethmoid cells, 

 blending anteriorly with the superior ; j^osfei-iorZ?/ it presents 

 the ope7iing of the sinuses of the head. The inferior meatus 

 is between the lower surface of the inferior turbinated bone 

 and the floor of the chamber ; it extends from the anterior 

 to the posterior naris, blending anteriorly and posteriorly 

 with the middle. The Schneiderian or pituitary mucous 

 membrane lines every part of the nasal chamber. It is 

 highly vascular and thick, performs the part of periosteum 

 to the turbinated bones and ethmoid lateral masses, and 

 assumes almost an erectile character at the anterior ex- 

 tremity of the ossa turbinata. The superior meatus is 

 supplied by the lateral nasal artery and nerve, and the 

 inferior and middle meatus by the spheno-palatine artery 

 and nerve. The ethmoid cells and the posterior part of 

 the nasal chamber, in addition, receive the fibres of the 

 olfactory nerve, which afford the special sense of smell. 

 These pass through the foramina in the cribriform plate of 

 the ethmoid bone, and are not enclosed in any common 

 sheath, but each fibre runs its course independently after 

 its origin from the olfactory bulb, and terminates in a cell 

 on the nasal mucous membrane. These fibres, examined 

 under the microscope, are found to resemble sympathetic 

 fibres, being devoid of medullary sheath and of white sub- 

 stance of Schwann. The septum nasi, at its antero- 

 inferior part, is continuous with the cartilage which fills 

 the incisive openings, and in which may be found a mucous 

 organ resembling the duct of Stenson, which in the ox forms 

 a communication between the nasal chamber and the cavity 

 of the mouth. In the horse it only opens into the nasal 

 chamber. ' We have traced it backwards above the bony 



