VAN 221: Veterinary Splanchnology and Applied Anatomy (1+1)

NASAL CAVITY (OX)

• The nasal cavity is the first section of the respiratory tract. It is a short tubular passage, wide in front and narrow behind, enclosed by the facial bones
• It is separated from the mouth by the palate and opens in front at the cranial nares or nostrils and caudally it opens into the pharynx through the caudal nares.
• The nostrils (nares) are two-left and right and are somewhat oval in outline and are placed obliquely so that they are closer together below than above
• They are situated at either end of the muzzle. They are bounded by two alae or wing and cranial part of the cartilaginous septum.
• The alae meet above and below forming commissures
• The superior commissure is narrow and the inferior one is wide and rounded
• The lateral alae are concave and medial one is convex above and concave below. The prominence of the medial alae is caused by the lamina of the alar cartilage
• The alar cartilage forms the dorsal wall by its lamina and the lateral wall by its cornua and a transverse bar looks like an anchor
• The medial wall is formed by the nasal septum.
• The skin on the dorsal and lateral wall is covered by hairs and the skin between and around the lining of the nostrils is devoid of hairs and is smooth, bare and moist
• There is no clear line of demarcation between the skin and nasal mucosa.
• The nasal cavity is short wide cranially and narrow behind. The nasal cavity is divided into two halves by an osseo-cartilaginous septum nasi
• The osseous part is formed by the perpendicular plate of the ethmoid, vomer and the cartilaginous part by the septal cartilage
• The surfaces of the cartilage form the internal walls of the nasal cavity
• The dorsal border is attached along the frontal and nasal sutures and extends beyond the apices of the nasal bones about two inches
• The nasal cavity is not completely divided by the septum nasi due to the fact that the caudal third of septum nasi is separated from the floor of the nasal cavity by an interval that increases from before backward
• The cavity is mostly occupied by the nasal and ethmo-turbinates
• It is divided into three passages or meatuses called as dorsal, middle and ventral nasal meatus.

(Click to peep inside the nasal cavity)

• The dorsal nasal meatus is a narrow passage between the roof of the nasal cavity and the dorsal turbinate bone
• Its caudal 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 is between the dorsal and ventral turbinate bones
• It is a very narrow passage and divides caudally into two branches by the intervention of the ethmoturbinates
• The ventral nasal meatus is situated between the ventral turbinate and the floor of the nasal cavity
• It is much larger than the other two and is the direct passage between nostrils and pharynx
• The opening of the vomero-nasal organ and incisive or naso palatine duct is situated in the floor of the cranial end of this meatus
• The common nasal meatus is situated between the nasal septum and the turbinates and is continuous laterally with the other meatuses. It is narrow dorsally but wider ventrally.
• The caudal nares or chonae are elliptical openings by which the nasal cavity and the pharynx communicate and situated in the same plane on the floor of the nasal cavity at its caudal extremity and are separated by the vomer.
• The nasal cavity is lined by mucous membrane, which is highly vascular
• In front, it is continuous with the skin lining the nostrils and behind with the mucous membrane of the pharynx
• The lower three-fourth of the mucous membrane is red in colour and forms the respiratory portion
• The upper fourth paler part forms the olfactory portion, which is responsible for smell.
• The ductus incisivus (naso-palatine duct) is a small mucous tube, which extends from the nasal cavity to the papilla incisive
• The nasal opening of this duct opens on the medial surface of the alar fold of the ventral nasal meatus