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 
Nasal 
proce SS of 
premaxilla the frontal and nasal sutures, and 
extends beyond the apices of the 
Nasal nasal bones about two inches (ca. 
bone 5em.). From this border a thin, 
narrow plate, the parietal cartil- 
Parietal age (Cartilago parietalis) curves 
cartilage outward for a short distance on 
: either side. Near the nostrils 
Lamina ‘ : 
ofalar these plates are somewhat wider, 
cartilage partially making good the defect 
ae (naso-maxillary notch) in the 
of alar bony wall of the cavity in this 
cartilage situation. The ventral border is 
thick and rounded; it lies in the | 
groove of the vomer and the pala- 
tine processes of the premaxillie; | 
its anterior part occupies the 
space between the premaxillary — 
Fig. 453.—Nasav CartiLtaces oF Horse; Dorsar View. bones. A process from it extends | 
1, Anterior extremity of cartilage of septum nasi; 2, foramen into the palatine fissure, which it } 
aaa 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 em.), 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 When 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. 
