510 



RESPIRATORY SYSTEM OF THE HORSE 



encloses the cartilaginous prolongation of the ventral turbinate bone.' The extrem- 

 ity of the cornu usually causes a slight projection of the skin a short distance behind 

 and below the inferior commissure. 



The muscles of the nostrils have been described (p. 258). 



Vessels and Nerves. — The arteries are branches of the palato-labial, superior 

 labial, and lateral nasal arteries, and the blood is conveyed away by corresponding 

 veins. The lymph vessels go to the mandibular lymph glands. The nerves are 

 derived from the infraorbital nerve (sensory) and from the facial nerve (motor) . 



The nasal cavity is divided into two symmetrical halves by the median septum 

 nasi (Figs. 452, 455, 456). The osseous septum (Septum nasi osseum) is formed 

 behind by the perpendicular plate of the ethmoid and ventrally by the vomer. A 

 few ridges on the former correspond to the ethmoidal meatuses. The major part 



of it, however, is formed by the 

 cartilage of the septum nasi (Car- 

 tilago septi nasi). The surfaces 

 of the cartilage are marked by 

 faint grooves for the vessels and 

 nerves which course over it. The 

 dorsal border is attached along 

 the frontal and nasal sutures, and 

 extends beyond the apices of the 

 nasal bones about two inches (ca. 

 5 cm.). From this border a thin, 

 narrow plate, the parietal cartil- 

 age (Cartilago parietalis) curves 

 outward for a short distance on 

 either side. Near the nostrils 

 these plates are somewhat wider, 

 partially making good the defect 

 (naso-maxillary notch) in the 

 bony wall of the cavity in. this 

 situation. The ventral border is 

 thick and rountled; it lies in the 

 groove of the vomer and the pala- 

 tine processes of the premaxillag; 

 its anterior part occupies the 

 space between the premaxillary 

 bones. A process from it extends 

 into the palatine fissure, which it 

 almost completely fills; the pala- 

 tine end of the process lies in the 

 submucous tissue of the hard palate, and the palatine artery turns medially between 

 the cartilage and the bone. The posterior border is continuous with the perpen- 

 dicular plate of the ethmoid bone.^ The alar cartilages are attached to the anterior 

 extremity by fibrous tissue in such a manner as to allow very free movement — in 

 fact an actual joint may be present. The ventral part of the cartilage is about 

 half an inch (ca. 1 cm.), the middle part about one-tenth of an inch (ca. 2.5 mm.), 

 and the dorsal part about a quarter to a third of an inch (ca. 6 to 8 mm.) in 

 thickness. 



1 "WTien the nostril is fully dilated it is circular in outline, and the so-called false nostril is 

 effaced by the lamina of the alar cartilage being brought in contact with the superior commissure. 



' The cartilage is to be regarded as an unossified part of the mesethmoid. It will be noted 

 that the line of demarcation between the bone and the cartilage is irregular and varies with age; 

 extensive ossification (or calcification) of the cartilage is commonly found in old animals. The 

 process often results in the formation of calcareous islands in the cartilage. 



Nasal 

 process of 

 -premaxilla 



Nasal 

 hone 



Parietal 

 cartilage 



Lamina 

 of alar 

 cartilage 



Cornu 

 of alar 

 cartilage 



Fig. 4.53, — Nas.vl C.4.htilages of Horse; Dorsal View. 

 1, Anterior extremity of cartilage of septum nasi; 2, foramen 



incisivum. 



