الفهرس 
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Abstract
The head of the dog has six cavities: oral, nasal, orbital, pharyngeal, auricular and cranial cavity. The current work was performed by the help of the gross anatomical sections and by the computed tomographical images.
The nasal cavity was divided by the nasal septum into two equal halves; right and left. The nasal cavity has two main opening; the external nasal opening and internal nasal opening named choana, which opened in the nasopharynx. The right and left nasal cavities are occupied by the nasal conchae, which are named according their topographic position into; dorsal, ventral, and ethmoidal nasal conchae.
The dorsal nasal concha is a simple elongated bony plate which occupies the rostral part of the nasal cavity. The ventral nasal concha is a simple, thick, tightly folded and short bony plate that occupies the rostral and ventral part of the nasal cavity.
The caudal part of the nasal cavity is almost occupied by the presence of the ethmoidal concha forming the ethmoidal labyrinth. Generally, the ethmoidal concha alone is larger than the other nasal concha, which is related to the high smelling sensation of the dog.
The nasal septum is composed of cartilage and bone, the cartilaginous part form the rostral ⅔ of this median septum. The dorsal border of the nasal septum is T-shaped and connected with the nasal and frontal bones, while its ventral border connected with the channel is formed by the vomer bone.
The paired vomeronasal organ is located in the rostral base of the nasal septum and partially is enclosed by a scroll of cartilage. The vomeronasal organ consisted of a pair of long ducts on each side of the longitudinal nasal septum at the ventral nasal meatus and is supported by a thin cartilage but was separated by the nasal septum.
The paranasal sinus system of the dog is poorly developed, if compared to other domestic animals. There are two paranasal sinuses; maxillary recess, and frontal sinus.
The maxillary sinus is a small recess and communicated freely with the nasal cavity and occupies the face rostral to the orbit and above the roots of the last three check teeth. The maxillary sinus extendes to the level of the rostral border of the 1st upper cheek tooth to the caudal border of the 3rd upper check tooth.
There is an oval wide oblique infra-orbital foramen, while the supra-orbital foramen is absent. The ventral border of the infra-orbital foramen was situated at the level of the rostral border of the 1st upper cheek teeth, while its dorsal border is situated at the level of the caudal border of the 3rd upper check teeth.
The frontal sinus is the largest sinus occupying the most of the frontal bone, including zygomatic process. The frontal sinuse extendes rostrally to the level of the rostral border of the 2nd upper cheek tooth.
The frontal sinus is divided into the left and the right sinuses by a regular longitudinal thick bony inter frontal septum. Each one of the frontal sinus is completely subdivided into two compartments; small rostral compartment and the large caudal compartment by a transverse, oblique and thick complete septum.
Each frontal sinus have two naso-frontal openings connecting the frontal sinus to the caudal half of the nasal cavity, The first opening is named the rostral naso-frontal opening located in the rostral portion of the small rostral compartment. The second opening is named the caudal naso-frontal opening that located in the rostral portion of the large caudal compartment.
There are two small diverticulum in the frontal sinus in the large caudal compartment; orbital diverticulum and caudal temporal diverticulum.
The soft palate is the caudal continuation of the hard palate into the pharyngeal cavity. It divides the rostral portion of the pharyngeal cavity into; dorsally situated nasopharynx and ventrally situated oropharynx.
The orbital cavity is an incomplete bony conical cavity that containes the eye ball with all its accessory structures named the ocular adnexa.
The cranial cavity is described as the most vital cavity in the head region, as it contains the brain with all important structures. The roof of the cranium consists of the parietal and the frontal bones, while the caudal wall is formed by the occipital bone; the lateral wall was consisted of temporal, parietal, frontal and the sphenoid bones, while the rostral wall is represented by the cribriform plate of the ethmoidal bone.
There are three auricular cavities; external, middle and internal ear cavity. The different section images of CT determine the some structures of the auricular cavity. The middle ear contains three auditory ossicles; malleolus, incus and stapedius bone.
The histological studies of the rostral part of nasal conchae reveals that the epithelial lining of the dorsal nasal concha is keratinized stratified squamous epithelium, which is interdigitated with the underlying lamina propria. There were numerous compound sero-mucous glands. The histological study reveals that the olfactory epithelium is comparatively thicker than that of respiratory region and comprises three cell types; basal cells, supporting (sustentacular) cells and bipolar (olfactory) cells.
The SEM of the vestibular region of the dorsal nasal conchae shows the wrinkled surface with numerous microvilli, and small openings of sebaceous and sweat galnds. While, the SEM of the vestibular region of the ventral nasal conchae shows lots of the microvilli which take the filiform-like microvilli.
The SEM of the respiratory proper region of the dorsal nasal conchae reveals that the surface have many longitudinal with a little number of the opening of the goblet cells and with magnification, the cilia of the cell appear as a rosette-shape, which with high magnification appeared to carry numerous microvilli. While, The SEM of the respiratory proper region of the ventral nasal conchae shows numerous cilia of the cell which cover all surface.
The SEM of the dorsal nasal conchae at the nasal fundus region appeared to have numerous microvilli of ciliated olfactory cells which with high magnification appeared to have the rod-like appearance. While, the ventral nasal conchae at the nasal fundus region has numerous long microvilli of the ciliated olfactory cells. ethmoidal nasal conchae appeared to have a dense network of long microvilli of ciliated olfactory cells covering its entire surface.