March 13, 2010
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Palatine Bone

The palatine bones are situated at the posterior part of the nasal cavity, between the maxillae and the pterygoid processes of the sphenoid bone (fig. 371). Each assists in forming the floor and lateral wall of the nasal cavity, the roof of the mouth, and the floor of the orbit, and enters into the formation of the pterygopalatine and pterygoid fossa and the inferior orbital fissure.

The palatine bone somewhat resembles the letter ‘L’, and consists of a horizontal and a perpendicular plate, and three outstanding processes - viz. the tubercle (pyramidal process), which is directed backwards, laterally and downwards from the junction of the horizontal and perpendicular plate, and the orbital and sphenoidal processes, which surmount the perpendicular plate and are separated by a deep notch, named the spbenopalatine notch.

Figure 391

The horizontal plate of the palatine bone (figs. 387, 392) is quadrilateral and has two surfaces and four borders. The nasal surface, concave from side to side, forms the posterior part of the floor of the nasal cavity. The palatine surface forms, with the corresponding surface of the opposite bone, the posterior one-fourth of the bony palate; near its posterior margin there is a curved ridge, termed the palaline crest. The posterior border is thin and concave ; to it, and to the palatine surface as far forwards as the palatine crest, the expanded tendon of the tensor palati (tensor veli palatini) is attached. The medial end of the posterior border is pointed and, when united with that of the opposite bone, forms a projecting process named the posterior nasal spine, for the attachment of the musculus uvulae.

Figure 392

The anterior border is serrated and articulates with the palatine process of the maxilla. The lateral border is united with the inferior border of the perpendicular plate and is grooved by the lower end of the greater palatine groove (pterygopalatine sulcus). The medial border, thick and serrated, articulates with the corresponding border of the opposite bone, and the opposed borders form the nasal crest, which articulates with the posteriorpart of the lower edge of the vorner and is continuous anteriorly with the nasal crest of the maxillae.

The perpendicular part of the palatine bone (figs. 392. 393), thin and of an oblong form, has two surfaces and four borders.

The nasal surface exhibits at its lower part a broad shallow depression which forms part of the inferior meatus of the nasal cavity. Immediately above this the conchal crest forms a horizontal ridge for articulation with the interior nasal concha ; still higher there is a second broad, shallow depression, which forms part of the middle meatus and is limited above by the ethmoidal crest for articulation with the middle nasal concha. Above the ethmoidal crest there is a narrow, horizontal groove, which forms part of the superior meatus.

Figure 393

The maxillary surface is rough and irregular throughout the greater part of its extent, for articulation with the nasal surface of the maxilla ; its upper and posterior part is smooth and forms the medial wall of the pterygopalatine fossa ; its front portion, which is also smooth, projects beyond the posterior border of the maxillary hiatus and forms the posterior part of the medial wall of the maxillary sinus (fig. 386). On the posterior part of the maxillary surface there is a deep vertical groove, named the greater palatine groove. (pterygopalatine sulcus), which in the articulated skull is converted into the greater palatine canal (pterygopalatine canal) by the maxilla; this canal transmits the greater palatine (descending palatine) vessels and nerves.

The anterior border is thin and irregular; at the level of the conchal crest a pointed projecting lamina is directed forwards below and behind on the maxillary process of the inferior nasal concha.. It articulates with the latter and assists in forming the medial wall of the maxillary sinus (fig. 386). The posterior border (fig. 393) is serrated for articulation with the medial pterygoid plate of the sphenoid bone. This border is continuous above with the sphenoidal process; it expands below into the tubercle (pyramidal process) of the palatine bone. The superior border supports the orbital process in front and the sphenoidal process behind. These processes are separated by the sphenopalatine notch, which is converted into the sphenopalaiine foramen by the under surface of the body of the sphenoid. In the articulated skull this foramen leads from the pterygopalatine fossa into the posterior part of the superior meatus of the nose, and transmits the spheuopalatine vessels and nerves. The inferior border is fused with the lateral border of the horizontal plate and, in front of the tubercle (pyramidal process), is marked by the lower end of the greater palatine groove.

The tubercle (pyramidal process) of the palatine bone projects backwards, laterally, and downwards from the junction of the horizontal and perpendicular plates of the bone, and fits into the angular interval between the lower ends of the pterygoid plates. On its posterior surface there is a smooth, grooved, triangular area, limited on each side by a rough articular furrow. The furrows articulate with the pterygoid plates, while the grooved triangular area completes the lower part of the, pterygoid fossa and gives origin to some fibres of the medial pterygoid muscle. The anterior part of the lateral surface is rough for articulation with the maxillary tuberosity ; the posterior part consists of a smooth triangular area, which appears, in the articulated skull, at the lower part of the infratemporal fossa between the maxillary tuberosity and the lateral pterygoid plate (fig. 320). In the base or inferior surface of the tubercle, close to its union with the horizontal plate of the bone, are the lesser palatine foramina for the transmission of the lesser (middle and posterior) palatine nerves (fig. 387).

The orbital process of the palatine bone (figs. 392, 393) is directed upwards and laterally from the front of the perpendicular plate, to which it is joined by a constricted neck. It encloses an air-sinus, and presents three articular and two non-articular surfaces. Of the articular surfaces, (1) the anterior or maxillary, of an oblong form, is directed forwards, laterally, and downwards, and articulates with the maxilla, (2) the posterior or sphenoidal, directed backwards, upwards and medially presents the opening of the air-sinus, which usually communicates with the sphenoidal sinus ; the margins of the opening articulate with the sphenoidal concha ; (3) the medial or ethmoidal directed medially and forwards, articulates with the labyrinth of the ethmoid bone. In some cases, the air-sinus opens on this surface and then communicates with the posterior ethmoidal sinuses ; more rarely it opens on the ethmoidal and sphenoidal surfaces, and then communicates with the posterior ethmoidal sinuses and the sphenoidal sinus. Of the non-articular surfaces : (1) the superior or orbital, triangular in shape, is directed upwards and laterally, and forms the posterior part of the floor of the orbit ; and (2) the lateral, of an oblong form; is directed towards the pterygopalatine fossa and is separated from the orbital surface by a rounded border, which forms the medial part of the lower margin of the inferior orbital fissure ; the lower part of this surface may present a groove directed laterally and upwards, which lodges the maxillary nerve and is continuous with the transverse groove on the upper part of the posterior surface of the maxilla (p. 315). The border between the lateral and posterior surfaces is prolonged downwards as the anterior boundary of the sphenopalatine notch.

The sphenoidal process of the palatine bone (figs. 392, 393) is a thin, compressed plate, smaller and on a lower level than the orbital process it is directed upwards and medially. Its superior surface articulates with the under surface, of the sphenoidal concha and the root of the medial pterygoid plate; it presents a groove which contributes to the formation of the palatinovaginal (pharyngeal) canal. The inferomedial surface is concave and forms a small part of the roof and lateral wall of the nasal cavity. The posterior part of the lateral surface articulates with the medial pterygoid plate; the anterior part is smooth and forms a portion of the medial wall of the pterygopalatine fossa. The posterior border is rough and articulates with the vaginal process of the medial pterygoid plate. The anterior border forms the posterior boundary of the sphenopalatine notch. The medial border articulates with the ala of the vomer.

The orbital and sphenoidal processes are separated from each other by the sphenopalatin notch, which is converted into the sphenopalatine foramen by the under surface of the body of the sphenoid ; sometimes the two processes are united by a spicule of bone which converts the notch into a foramen.

Ossification.-The palatine bone is ossified in membrane from one centre, which appears during the eighth week of fetal life in the perpendicular plate of the bone. From this point ossification spreads upwards into the orbital and sphenoidal processes, medially into the horizontal plate, and downwards into the tubercle (pyramidal process).

At the time of birth the height of the perpendicular plate is about equal to the transverse width of the horizontal plate, whereas in the adult it measures nearly twice as much.