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 dorsal 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 
en Dorsal Ethm Senate Te 
entra ; oat eptum between 
turbinate Middle turbinate Dorsal turbinates psiart sinuses 
Ventral meatus meatus 
Fic. 454.—Nasat Cavity or Horse; Sacirrar Section wire Seprum ReMoveD. 
1, Dorsal turbinate fold; 2, alar fold, containing cartilaginous prolongation of ventral turbinate; 3, arrow pointing 
to naso-maxillary opening, which is concealed by dorsal turbinate bone; 4, 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 middle 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 
ptum 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 posterior 
art (fundus) of the nasal cavity. Between the ethmoturbinates, of which each 
