Vasoconstriction and diminished secretion, arise from the superior cervical

ganglion via the nerve of the pterygoid canal to the pterygopalatine ganglion.

Parasympathetic fibres, which produce vasodilatation and increased secretion,

are carried in the greater superficial petrosal nerve and the nerve of the

pterygoid canal to the pterygopalatine ganglion from which postganglionic fibres

are distributed.

The olfactory nerves - some twenty filaments - derive from the olfactory bulb,

enter the nasal cavity through the cribriform plate of the ethmoid, and are

distributed in a network in the mucous membrane in the upper third of the nasal

septum and the lateral wall of the nasal cavity. The perineural sheaths of these

filaments communicate directly with the pia-arachnoid and thus may transmit

Infection to the meninges.

The paranasal sinuses

The paranasal sinuses, arranged in pairs and in relation to each nasal cavity,

comprise two groups, anterior and posterior (Fig. 22, 23). The former includes

the maxillary sinus, the frontal sinus and the anterior ethmoidal cells, all of

which communicate with the middle meatus. The posterior group consists of the

posterior ethmoidal cells and the sphenoidal sinus communicating with the

superior meatus.

The maxillary sinus is also known as the maxillary antrum. It exists at birth as

a small but definite cavity adjacent to the middle meatus, and it enlarges

gradually to reach its maximum dimensions about the twenty-first year with the

eruption of the upper wisdom tooth. The sinus expands in the maxilla during the

eruption of the primary dentition until it reaches the level of the floor of the

nasal cavity about the seventh year. In adult life it is somewhat pyramidal in

shape, its roof being formed by the floor of the orbit, its floor being in close

proximity to the roots of the second dentition; its posterior wall lying in

relation to the pterygopalatine fossa; its medial wall adjoining the lateral

wall of the nasal cavity; and its anterolateral walls being superficial. The

opening into the middle meatus, the maxillary ostium, is near the upper part of

the cavity of the sinus, and is thus unfavourably placed for drainage. There may

be one or more accessory ostia posterior to the main one.

The frontal sinus is rudimentary at birth, being represented by a small upward

prolongation from the anterior end of the middle meatus, the nasofrontal duct.

During childhood this duct enlarges upwards to reach the level of the orbital

roof about the ninth year. Thereafter the sinus extends for a variable distance

as a result of absorption of cancellous bone between the outer and inner tables

of the frontal bone. The anterior wall is formed by the outer table; the

posterior wall is related to the inner table which separates it from the frontal

lobe of the brain; its floor forms part of the orbital roof; and the medial wall

is a septum separating the two frontal sinuses. The opening of the frontal sinus

is in its floor, and communicates with the middle meatus through the nasofrontal

duct.

The ethmoid sinuses constitute a cell labyrinth and are present at birth as

prolongations of the nasal mucosa into the lateral mass of the ethmoid bone. In

adult life they vary in number, size and shape, and for clinical purposes they

are classified as anterior and posterior, depending upon whether they

communicate with the middle or the superior meatus. Medially the cell labyrinth

lying in relation to the upper half of the nasal cavity, laterally - to the

orbit, from which the cells are separated laterally by the lamina papyracea and

to the maxillary sinus. The cells abut anteriorly on the frontal process of the

maxilla, posteriorly they are related to the sphenoid sinus. Superiorly the

ethmoid cells related to the frontal sinus and anterior cranial fossa.

The sphenoid sinus occupies the body of the sphenoid bone, and may be present at

birth as a small indentation of nasal mucosa. The sinus varies greatly in size