512 RESPIRATORY SYSTEM OF THE HORSE 



mass IS composed, there are three principal and numerous small passages, the 

 ethmoidal meatuses (Meatus ethmoidales) . 



The choanae or posterior nares are two elliptical orifices by which the nasal 

 cavity and pharynx commmricate. They are in the same plane as the floor of the 



Parotid ExUrnal Mandibular 



duct maxillary lymph glands 



vessels 



Fig. 455. — Cross-section of He.^d of Horse. 

 The section is cut midway between the medial canthus and the anterior end of the facial crest and is a front view. 

 1, Septum nasi; 2, 3, 4, dorsal, middle, and ventral meatus nasi; 5, common meatus nasi; G, cavity of dorsal 

 turbinate bone (i. e., turbinate part of frontal sinus) ; 7, cavit\' of ventral turbinate bone (i. c, turbinate part of maxillary 

 sinus); .'^, maxillary .sinus; 9, communication between 7 and S over infraorbital canal; 10, naso-lacrimal duct; 11, 

 infraorbital nerve and canal; 12, m. levator labii superioris proprius; 13, mouth cavit.v; 14, palatine artery; 15, fifth 

 upper cheelc tooth {posterior part) ; 16, sixth lower cheek tooth (anterior part) ; 17, m. buccinator; IS, hard palate; 19, 

 vena reflexa; 20, superior buccal glands; 21, buccinator vessels and nerve; 22, alveolar vessels and nerve of mandible; 

 23, lingual arter.v; 24, mm. genio-glossi ; 25, m. hj-o-glossus (number placed between two radicles of lingual vein); 26, 

 m. st.vlo-glossus; 27, m. mylo-hyoideus; 2.S, m. genio-hyoideus; 29, lingual ner\'e; 30, h,\'poglossal nerve; 31. sub- 

 lingual artery; 32, m. digastricus (anterior belly). The mandibular duct is shown in the fat lateral to the genio-hyoideus 

 but is not marked. 



nasal cavity, and are separated from each other by the vomer. They are, taken 

 together, about two inches (ca. 5 cm.) wide and three to four inches (ca. 8 to 10 

 cm.) long. 



The nasal mucous membrane (Membrana mucosa nasi) is thick, highly vas- 

 cular, and is, in general, firmly attached to the underlying periosteum and peri- 



