72 



THE SKELETON OF THE HORSE 



The septum nasi is incomplete in the macerated skull. It is formed by the 

 perpendicular plate of the ethmoid behind, and the vomer below. In the fresh 

 state it is completed by a plate of cartilage. 



The superior meatus (Meatus nasi superior) is a narrow passage between the 

 roof and the superior turbinal bone. It ends at the cribriform plate of the ethmoid. 

 The middle meatus (Meatus nasi medius) is the space between the two turbinal 

 bones. In its posterior part is the very narrow opening into the maxillary sinus. 

 The inferior meatus (Meatus nasi inferior) is the channel along the floor which is 

 overhung by the inferior turbinal bone. It is much the largest and is the direct 

 path between the anterior and posterior nares. 



The external aperture is bounded by the nasal bones and the premaxillaj. 



Fig. 37. — Cross-section of Nasal Region op Skull 

 OF Horse; the Section Passes Through 

 THE Anterior End of the Facial Crest, 

 and Between the Third and Fourth Cheek 

 Teeth. 



a, Superior, b, inferior turbinal bone; c, d, cavi- 

 ties of o and 6; e, common meatus; /, g, h, superior, 

 middle, inferior meatus; !, k, passages to cavities of 

 turbinal bones; 1, naso-lacrimal duct; m, infraorbital 

 canal; n, anterior end of maxillary sinus; o, septal 

 cartilage. (After Ellenberger, in Leisering's Atlas.) 



Fig. 38. — Cross-section of Nasal Region of Skull 

 OF Horse; the Section is Cut About Half- 

 way between the Orbit and the Anterior 

 End of the Facial Crest, and Passes be- 

 tween the Fifth and Sixth Cheek Teeth. 

 a, Superior, 6, inferior turbinal bone; c, d, cavi- 

 ties of a and b; e, common meatus; /, superior, g, 

 middle, h, inferior meatus; ?', placed over ridge in 

 maxillary sinus; k, communication between outer and 

 inner (turbinal) part of maxillary sinus; I, naso- 

 maxillary opening; m, naso-lacrimal canal; n, infra- 

 orbital canal. (After Ellenberger, in Leisering's Atlas.) 



The posterior extremity or fundus is separated from the cranial cavity by the 

 cribriform plate of the ethmoid, and is largely occupied by the lateral masses of 

 that bone. 



THE PARANASAL SINUSES 



Connected directly or indirectly with the nasal cavity, of which they are diver- 

 ticula, are four pairs of air-sinuses (Sinus paranasales), viz., maxillary, frontal, 

 spheno-palatine, and ethmoidal. 



The maxillary sinus (Sinus maxillaris) is the largest. Its external wall is 

 formed by the maxilla, the lacrimal, and the malar. It is bounded internally by 

 the maxilla, the inferior turbinal, and the lateral mass of the ethmoid bone. It 

 extends backward to a transverse plane in front of the root of the supraorbital 

 process, and its anterior limit is indicated approximately by a line drawn from the 

 anterior end of the facial crest to the infraorbital foramen. Its upper boundary 

 corresponds to a line drawn l)ackward from the supraorbital foramen parallel to 

 the facial crest. The floor is formed l)y the alveolar part of the maxilla; it is very 

 irregular and is crossed by bony plates running in various directions. The last 



