Nasal Cavity and Paranasal Sinuses

Hello, in this post we’ll take a look at the external and internal features of the nasal cavity as well as the species differences in the arrangement of the paranasal sinuses.

The Nasal Cavity 

The nose includes the external nares and associated cartilages, the nasal cavity and paranasal sinuses. It consists of the nasal bones dorsally; the maxillae laterally; the palatine, incisive and maxillae bones ventrally; while the cribriform plate of the ethmoid bone forms the caudal limit. A rostral continuation of the crista galli of the ethmoid bone creates the median septum.  

The nasal cavity consists of the two external nares which lead to two nasal vestibules that are separated by the median nasal septum. These vestibules merge caudally and form a large nasal cavity which is lined with ciliated nasal mucosa. These cilia waft mucus and debris to the choanae (the paired openings between the nasal cavity and the nasopharynx) to be swallowed. Within the nasal cavity are nasal conchae which project medially from the walls of the cavity. They increase the respiratory surface area and are more complex in animals with highly developed olfaction. These conchae also have an extensive network of anastomosing vascular plexuses.

Externally, the nares are surrounded by hairless skin, except in the horse and humans, and form a structure which differs between species. In carnivores and small ruminants, a nasal plate exists and this is divided by a median groove called the philtrum. In large ruminants a nasolabial plate exists while in pigs a rostral plate is present and this is used to dig for food. The nares are supported by nasal cartilages which form the moveable part of the muzzle. In horses, which are obligate nasal breathers, the nares are held open by wing-like extensions known as the alar cartilages. The deeper parts of the nasal cavity are formed from the nasal and incisive bones.  

Paranasal Sinuses

The paranasal sinuses are cavities in the skull bone that are lined with mucous membranes and communicate with the nasal cavity. The size of the sinuses increase with age and are well developed in the horse and ox. The functions of the paranasal sinuses include:

• Mechanical and thermal protection of the orbit and cranial cavities 
• Increased skill dimensions for muscle attachment without increasing the weight of the skull 
• Resonance for vocalisation.

Several paranasal sinuses exist, including: maxillary, frontal, palatine, sphenoid, lacrimal (in pigs and ruminants), dorsal conchal sinus, ventral conchal sinus (in the pig, ruminants and horse), and the ethmoid cellules (in pigs and ruminants). The characteristics of these sinuses may differ between species.

Canine

The sinuses in dogs are relatively poorly developed and will vary according to the size and shape of the skull as well as with age. The frontal sinus has three compartments: the rostral, medial and lateral divisions, that are connected via ethmoidal meatuses. The lateral division is the largest. Dogs also have a maxillary sinus which is very large and lies above the roots of the molars.

Feline

The arrangement of the sinuses in cats is similar to that in dogs except that the frontal sinus is fused and has no divisions.

Porcine

The maxillary, frontal, lachrymal, shenoidal and conchal sinuses are quite prominent features of the skull and are there to protect the brain. In addition, pigs have very well developed nasal conchae, extensive olfactory mucosa and an excellent sense of smell.

Equine

The horse sinuses are extensive and are vulnerable to infection and offer potential surgical access to the roots of the molars. The frontal sinus communicates with the nasal cavity via the caudal maxillary sinus. The sinuses in the horse grow and their positions change with the jaw and teeth as the animal ages.

Bovine

The bovine sinuses are extensive and may continue into the base of the horn by the corneal process. Just like in the horse, the size and position of the sinuses changes with age.

That’s all for this post, see you next time :)