At the anterior end of the medial wall of the infratemporal fossa the lateral pterygoid plate is separated from the maxilla by the pterygomaxillary fissure, which leads into the small pterygopalatine fossa. At the bottom of the fissure, the pyramidal process of the palatine bone articulates with the lateral pterygoid plate and maxilla closing off the fissure and forming the narrow floor of the pterygopalatine fossa (Fig. 6.13). The roof is the body of the sphenoid. Medially the fossa is walled in by the perpendicular plate of the palatine bone (Fig. 6.25), part of the lateral wall of the nose (Fig. 6.31A). This plate splits at the top into an orbital process and a sphenoidal process which, with the roof of the fossa, bound the sphenopalatine foramen that communicates with the nasal cavity.
The perpendicular plate articulates anteriorly with the maxilla and between the two lies the greater palatine canal which opens below at a foramen on the hard palate. The posterior wall of the maxilla forms the anterior wall of the fossa, which is interrupted at the top by the medial end of the inferior orbital fissure that opens into the orbit. The pterygopalatine fossa is bounded posteriorly by the sphenoid bone (root of the pterygoid process containing the pterygoid canal and greater wing containing the foramen rotundum; Fig. 6.26).
Figure 6.25 Left palatine bone, from behind.
Figure 6.26 Partly disarticulated sphenoid bone, from the front.
The fossa contains the maxillary vessels and nerve and the pterygopalatine ganglion and fat (Fig.
6.21). The ganglion sends branches into the nose, palate and nasopharynx. The maxillary nerve supplies the posterior, upper teeth and passes forwards into the orbit. Branches of the maxillary vessels accompany all these nerves.
Maxillary nerve
The maxillary nerve, giving a meningeal branch to the front of the middle cranial fossa, passes through the foramen rotundum in the greater wing of the sphenoid bone into the pterygopalatine fossa.
Deviating laterally in the inferior orbital fissure for about 1 cm, it turns forwards to enter the infraorbital groove and canal in the floor of the orbit, changing its name to the infraorbital nerve and eventually emerging from the front end of the canal at the infraorbital foramen to supply skin on the face (see p. 354). The zygomatic nerve arises from the maxillary in the fossa and runs above the maxillary in the inferior orbital fissure to enter the orbit (see p. 402). The posterior superior alveolar nerve is also given off in the fossa. It passes through the pterygomaxillary fissure on to the posterior wall of the maxilla (see p. 364).
In the fossa the maxillary nerve is connected to the pterygopalatine ganglion by two branches that carry fibres going both to and from the ganglion.
Pterygopalatine ganglion
The pterygopalatine ganglion is a relay station between the superior salivary nucleus in the pons and the lacrimal gland and mucous and serous glands of the palate, nose and paranasal sinuses. It is the ganglion of hay fever (‘running nose and eyes’). Its connections are summarized on page 22.
The ganglion lies immediately in front of the opening of the pterygoid canal and the nerve of that canal runs straight into the back of the ganglion. The canal is below and medial to the foramen rotundum (Fig. 6.26), and so is the ganglion in relation to the maxillary nerve.
The autonomic root is the nerve of the pterygoid canal (Vidian nerve). This nerve is formed in the foramen lacerum by union of the greater petrosal nerve (see p. 417), containing mainly parasympathetic secretomotor fibres, with the deep petrosal nerve, containing sympathetic vasoconstrictor fibres. The former is a branch of the facial nerve and the latter is a branch from the internal carotid sympathetic plexus. The combined nerve passes forward in the pterygoid canal and joins the ganglion.
The postganglionic secretomotor fibres to the lacrimal gland leave the ganglion and join the maxillary nerve, pass in its zygomatic branch into the orbit, join the lacrimal branch of the ophthalmic nerve and so reach the lacrimal gland.
The rest of the fibres in the connections between the maxillary nerve and the ganglion are sensory and, like the sympathetic fibres in the deep petrosal nerve, they pass through the ganglion without relay.
The only cell bodies in the ganglion are parasympathetic (secretomotor). The branches of the pterygopalatine ganglion are distributed to the nose, palate and nasopharynx. Every branch carries a mixture of all three kinds of fibres: sensory, secretomotor and sympathetic.
Medial posterior superior nasal nerves pass through the sphenopalatine foramen, cross the roof of the nose, and are distributed to the septum. The largest of these is termed the nasopalatine nerve, as it continues beyond the septum through the incisive canal to supply the anterior part of the hard palate.
The lateral posterior superior nasal nerves pass through the sphenopalatine foramen and turn forward to supply the posterosuperior part of the lateral wall of the nose.
T h e greater palatine nerve passes down through the greater palatine canal, between the
perpendicular plate of the palatine bone and the maxilla (Fig. 6.27). At the greater palatine foramen it turns forward to supply the mucous membrane of the hard palate. As it descends it also supplies the posteroinferior part of the lateral wall of the nose and the medial wall of the maxillary sinus.
Figure 6.27 Right trigeminal and geniculate ganglia, petrosal nerves and pterygopalatine and otic ganglia, from the right. Much of the right side of the skull has been removed, including most of the maxillary sinus, leaving only its medial wall.
The lesser palatine nerves, two in number, pass down behind the greater palatine nerve and emerge through the lesser palatine foramina. They pass back to the soft palate and the mucous membrane of the palatine tonsil. They carry the only non-secretomotor fibres transmitted in the greater petrosal nerve; these are sensory (taste) fibres that have their cell bodies in the genicular ganglion of the facial nerve.
The pharyngeal nerve passes back through the palatovaginal canal (a little canal between the vaginal process of the medial pterygoid plate and the sphenoidal process of the palatine bone) and supplies the mucous membrane of the nasopharynx. A few fine orbital branches enter the orbit via the inferior orbital fissure and supply periosteum of the orbital floor and the mucous membrane of the sphenoidal and ethmoidal sinuses.
Maxillary vessels
The maxillary artery passes through the pterygomaxillary fissure, enters the pterygopalatine fossa in front of the ganglion and gives off five branches. These and the artery's further course into the orbit are described on page 363. The branches of the maxillary artery in the pterygopalatine fossa may be ligated by an approach through the maxillary sinus (see p. 376), the fossa being entered instrumentally through the posterior wall of the sinus. An alternative endoscopic approach is via the sphenopalatine foramen.
Veins accompany the above arteries and, passing through the fossa, emerge at the pterygomaxillary fissure to drain into the pterygoid plexus. In general, vessels in the fossa lie anterior to the nerves.