THE NASAL CAVITY 



511 



The two turbinate bones project from the lateral wall, and divide the outer 

 part of the cavity into three meatuses— dorsal, middle, and ventral (Figs 454 

 455,456). 



The dorsal nasal meatus (Meatus nasi dorsalis) is a narrow passage, bounded 

 dorsally by the roof of the cavity, and ventrally by the ventral turbinate bone; its 

 posterior end is closed by the junction of the inner plate of the frontal bone with the 

 cribriform plate and lateral mass of the ethmoid. It transmits air to the olfactory 

 region. 



The middle nasal meatus (Meatus nasi medius) is between the two turbinate 

 bones. It is somewhat larger than the dorsal meatus, and does not extend back 

 so far; it ends near the great ethmoturbinate and the ethmoidal meatuses. In 

 its posterior part is the extremely narrow, slit-like interval by which the max- 

 illary sinus communicates with the nasal cavity — the naso-maxillary opening 

 (Aditus naso-maxillaris). The opening, which is normally a mere fissure, is not 

 visible from the nasal side, being concealed by the overhanging dorsal turbinate. 

 A fine flexible probe, passed outward and somewhat backward between the turbinate 



Ventral 

 meatus 



Ventral 

 turbinate 



Dorsal 

 turbinate 



litlimo- Septum between 

 Dorsal turbinates frontal sinuses 



Fig. 454. — Nasal Cavity of Horse; S.igittal .Section with Septum Removed, 

 1, Dorsal turbinate fold; ^, alar fold, containing cartilaginous prolongation of ventral turbinate; 3, arrow pointing 

 to naso-maxillary opening, wliich is concealed by dorsal turbinate bone; J/, cranial cavity; 5, sphenoidal sinus; 6, 

 hamulus of pterygoid bone. The olfactory mucous membrane is shaded. Dotted lines indicate anterior limit of 

 uncoiled parts of turbinate bones, which inclose parts of frontal and maxillary sinuses. 



bones, enters the maxillary sinus; if introduced a little further in the same direction, 

 it usually passes through the orifice of communication between the maxillary 

 sinus and the frontal sinus and enters the latter. A small part of the fissure usually 

 brings the anterior division of the maxillary sinus into communication with the 

 nasal cavity. The spaces enclosed by the coiled parts of the turbinates also open 

 into the riiiddle meatus. This passage may be characterized as the sinus-meatus, 

 but it also conducts air to the olfactory region. 



The ventral nasal meatus (Meatus nasi ventralis) is situated between the 

 ventral turbinate and the floor of the cavity. It is much larger than the other two, 

 and is the direct passage between the nostrils and the pharynx. The small, slit- 

 like orifice of the vomero-nasal organ and the incisive or naso-palatine duct is 

 situated in the floor of the anterior end of the meatus. 



The common nasal meatus (Meatus nasi communis) is situated between the 

 septum and the turbinates, and is continuous laterally with the other meatuses. 

 It is very narrow dorsally, but widens ventrally. 



The lateral masses of the ethmoid bone project forward into the poeterior 

 part (fundus) of the nasal cavity. Between the ethmoturbinates, of which each 



