**2.2 The maxillary sinus**

In the horse and donkey, the maxillary sinus divides into rostral and caudal compartments via a thin incomplete bony septum in the donkey or a complete septum in horse. The dorsal part of the septum was designed by the bulla of the ventral conchal

#### *Anatomical Guide to the Paranasal Sinuses of Domestic Animals DOI: http://dx.doi.org/10.5772/intechopen.106157*

sinus. This septum angles obliquely caudally and its rostral aspect is varied in with regards to location; it usually crosses the roots of the second and third molar teeth, approximately 4–5 cm caudal to the rostral end of the facial crest. Most specimens have a septum measuring around 1.5 cm high, whilst the sinus can be 4–5 cm deep with bony spicules [11]. The caudal maxillary sinus is incompletely divided by the infraorbital canal into lateral and medial compartments. The canal also facilitates free communication between the two parts. Only the third maxillary molar tooth root embeds in the caudal maxillary sinus. The rostral and caudal maxillary sinuses connect with the middle nasal meatus via a slit-like nasomaxillary opening. The capacious caudal maxillary sinus appears larger than the smaller rostral maxillary sinus. The rostral maxillary sinus communicates with the ventral conchal sinus via the wide conchomaxillary opening dorsal to the infraorbital canal. The opening of which located at the level of the rostral part of the first molar tooth until the caudal part of the second molar tooth. The rostral maxillary sinus is around 4–5 cm long and 0.3–0.4 cm wide (**Figures 1**–**3**) [11, 13]. When CT imaged, the maxillary sinus is low in density but has high-density structures; the infraorbital canal, maxillary septum and bony spicules.

In cattle and buffalo, the maxillary sinus excavates into the maxillary and lacrimal bones. The sinus cavity is triangular in shape as the base is located caudally with a cranial apex behind the infraorbital foramen. The cavity extends rostrally towards the facial tuberosity at the level of the caudal border of the second premolar tooth. Around 2-3 cm ventral to the orbit and caudal to third molar tooth, the sinus continues caudally into the lacrimal bulla which has thinner walls and the zygomatic bone [4]. The dorsal limit of the cavity is determined by a line extending from the infraorbital foramen to the medial canthus of eye, while the ventral limit is around 1–2 cm above the alveolar border. Under computed tomography imaging, the more dense infraorbital canal and bony spicules of the maxillary sinus are observed. The maxillary sinus communicates with the caudal part of middle nasal meatus in common with the palatine sinuses through the nasomaxillary opening. This opening is positioned on the medial wall just ventral to the nasolacrimal canal, over the infraorbital canal and at around the midpoint between the orbit and facial tuber at a level from the first molar to third molar teeth. The maxillary and palatine sinuses communicate through an oval maxillopalatine opening, located above the infraorbital opening at a level from second premolar to the second molar teeth [4]. Caudally, it also communicates with the lacrimal sinus through maxillolacrimal opening. There is a rostral crest within the maxillary sinus (**Figure 4**).

In camels, the maxillary sinus is in an excavation of a small part of the maxillary bone and the rostral part of the zygomatic bone. The maxillary sinus extends towards the level of the rostral border of the third upper cheek tooth. The medial boundary is formed by the osseous nasolacrimal canal and it communicates dorsally with the lacrimal sinus and with the caudal part of the middle nasal meatus via the nasomaxillary opening which in turn is partly covered by the lateral part of the dorsal conchal sinus [6].

In sheep and goats, the maxillary sinus is located in a triangular excavation of the maxillary bone and rostral part of the zygomatic bone. The sinus extends to the level of the rostral border of the third upper cheek tooth and rostral to the facial tuberosity. The sinus is incompletely separated by the infraorbital canal, therefore presenting as a smaller dorsomedial part and a larger ventrolateral part, [14]. Caudally, the sinus become larger and extends by the lacrimal bulla. This lacrimal bulla presents as dorsal and ventral orbital diverticula inside the orbital cavity. The sinus communicates dorsally with the lacrimal sinus by the maxillolacrimal opening, whilst the caudal section of the sinus communicates with the palatine sinus via the maxillopalatine opening on the medial side of the infraorbital canal. In addition, the sinus communicates with

the caudal part of the middle nasal meatus via the nasomaxillary opening which is partially covered by the lateral part of the dorsal nasal conchal sinus at the level of the fourth cheek tooth (**Figure 5**) [14].

In the dog and cat, in contrast to the other domestic mammals, the canine maxilla has no paranasal sinus, but rather a laterally directed outpouching, the maxillary recess.

#### **2.3 The sphenoidal sinus**

In the horse and donkey, the sphenoidal and palatine sinuses communicate with each other. The sphenopalatine sinuses are excavated into the palatine and sphenoid bones ventromedial to the orbit and ventral to forebrain [11]. There is a septum separating the left and right sphenoidal sinuses, however, it is not frequently in the midline. The dorsal and lateral walls of the sphenopalatine sinus are thin. The sinus communicates with the caudal maxillary sinus via the sphenopalatinal opening, which is the most caudal opening of the maxillary sinus. The opening itself appears sagittal oblique and is located between the caudal origin of the infraorbital canal and the pterygopalatine fossa, caudal to the last molar tooth roots (**Figure 2** structures 5 and 33 [13]).

In cattle and buffalo, the sphenoid sinus is shallow and excavated in the body and wing of the sphenoid bone [4]. The right and left sinuses are divided by a septum forming unequal small parts, the rostral canal and caudal cavity. It opens into the ethmoidal meatus via the nasosphenoidal opening.

In camels, the sphenoidal sinus is in a cavity within the body and wing of the sphenoidal bone. The sinus contains bony plates which subdivide it into small compartments, which alongside the frontal sinus compartments encircle the cranial cavity [6]. The sphenoidal sinus opens directly into the nasal fundus through the nasosphenoidal opening [6].

In the dog and cat, in some cases a sphenoidal sinus develops but not always.

#### **2.4 The ethmoidal sinus**

In cattle and buffalo, the ethmoidal cells are small cavities in the medial wall of the orbit [4]. The ethmoid bone forms the medial wall whereas their lateral walls are formed by the frontal, palatine and the wing of presphenoid bones. The ethmoidal cells open into the ethmoidal meatus.

In camels, the ethmoidal sinus is apparent in the ethmoid labyrinths. It communicates directly with the ethmoidal meatus into the nasal fundus [6].

In sheep and goats, the ethmoidal sinus is located at the nasal fundus part of the nasal cavity [14]. The ethmoidal sinus is apparent in the five triangular projections of the ethmoidal labyrinths. It communicates directly with the ethmoidal meatus into the nasal fundus.

#### **2.5 The lacrimal sinus**

In cattle and buffalo, the lacrimal sinus is a small excavation in the lacrimal and frontal bones rostromedial to the orbit. The lacrimal bones forms the lateral wall and the lateral mass of the ethmoidal bone forms the medial wall. The sinus cavity is not divided by osseous plates and the nasolacrimal canal traverses its lateral wall. It communicates with the maxillary sinus via maxillolacrimal opening (**Figures 5** and **6**).

In camels, the lacrimal sinus is occupies a small cavity in the lacrimal bone rostromedial to the orbit. The lacrimal bone forms the lateral wall, while the lateral mass of *Anatomical Guide to the Paranasal Sinuses of Domestic Animals DOI: http://dx.doi.org/10.5772/intechopen.106157*


#### **Table 1.**

*The paranasal sinuses in a range of mammals.*

the ethmoidal bone forms the medial wall. The lacrimal sinus is separated rostrally from the maxillary sinus by the nasolacrimal canal and it communicates with the maxillary sinus via the maxillolacrimal opening, just anterior to the orbital cavity at the level of third cheek tooth [6].

In sheep and goats, the lacrimal sinus is occupies a small cavity in the lacrimal bone rostromedial to the orbit. The lateral wall is formed by the lacrimal bone, while the medial wall is formed by the lateral border of the dorsal lamellae of the ventral nasal conchae [14]. It is separated rostrally from the maxillary sinus by the nasolacrimal canal and communicates with the maxillary sinus via the maxillolacrimal opening just anterior to the orbital cavity at the level of the third cheek tooth (**Figure 5**).

#### **2.6 The palatine sinus**

In cattle and buffalo, the palatine sinus appears larger than the maxillary sinus and is located within the horizontal part of the palatine bone and the palatine process of maxillary bone. The right and left palatine sinuses are separated by a median interpalatine septum, which is undulant caudally. The sinus extends from the caudal border of the palatine bone and rostral border of the orbit roughly 2 cm caudal to the third molar tooth to around 3–4 cm rostral to the first premolar teeth [4]. The sinus cavity contains an incomplete transverse bony crest which arises from the floor of sinus and subdivides the sinus into two unequal compartments. The caudal part of the sinus is traversed obliquely by the infraorbital canal that divides it into medial and lateral compartments. The palatine sinus communicates with the maxillary sinus via a maxillopalatine opening over the infraorbital canal (**Figure 6**).

In sheep and goats, the palatine sinuses are located within the horizontal part of the palatine bone and the palatine process of the maxillary bone, and it is the smallest sinus. The right and left palatine sinuses are separated by a median inter-palatine septum [14]. The sinus extends from the caudal border of the palatine bone and rostral border of the orbit caudal to the third molar tooth. The palatine sinus communicates with the maxillary sinus by the maxillopalatine opening over the infraorbital canal (**Table 1**) [3].
