The Palatine Bone
The palatine bones are two small bones of the skull which together form the rearmost section of the hard palate (roof of the mouth within the oral cavity).
They also form part of the floor and sides of the nasal cavity and extend to the orbit of the eye forming a small section of the orbit.
The palatine bones, like many bones in the human body, are paired bones named either left or right and they articulate (join together) along the central plane of the skull. In addition to joining with each other, the palatine bones also articulate with many other bones of the skull and are attached to connective tissue, muscles and tissues of the soft palate and nasal cavity. These bones have a distinctive shape but are probably among the least recognised outside of the medical profession and if a model of a human skeleton were offered as a three-dimensional jigsaw puzzle, the palatine bones would probably be the parts to cause the most problems.
The main features of the palatine bones are their incredibly complex shapes and in trying to understand the specific reasons for these shapes, it is always necessary to consider the bones when they are occupying their normal place within the skull and their relationship to all other parts of the skull.
Palatine Bone Definition
A palatine bone is defined as one of a pair of irregularly shaped bones located behind the maxilla which enters into the formation of the hard palate, nasal cavity and the floor of the orbit. The name originates from the word palate which is a direct translation from the Latin word palatum. The suffix -ine simply means “belonging to”. The correct Latin anatomical name for this bone is os palatinum.
Palatine Bone Location in the Skull
The precise position of the palatine bones is determined by other bones of the skull and a palatine bone articulates (joins) with six other bones these being the sphenoid, ethmoid, maxilla, inferior nasal concha, voma and the opposite palatine bone. They extend from the oral cavity to the nasal cavity and also reach and form part of the orbit of the eye.
Description of the Palatine Bone
The palatine bone is a complex shape and not easy to describe. The best way to understand its structure is by referring to suitable illustrations such as those found in the 1918 edition of Gray’s Anatomy of the Human Body.
The bone is generally similar in shape to a capital “L” with the left and right palatine bones mirroring each other and articulating at the centre of the rear part of the palate. The two main parts of the “L” shape are usually referred to as the horizontal plate (pars horizontalis) for the bottom of the “L” and the vertical part (pars perpendicularis), or perpendicular part, for the upright part of the “L”.
In addition to the two main parts, the palatine bone also has three outstanding processes or projections these being: the pyramidal process, the orbital process and the sphenoidal process. The orbital and sphenoidal processes are located on the uppermost section of the vertical part and are separated by the sphenopalatine notch and the pyramidal process is located at the rear being attached close to the junction between the horizontal and vertical parts.
The palatine bone is positioned at the rear part of the nasal cavity between the maxilla and the pterygoid process of the sphenoid and it contributes to the formation of three cavities these being the nasal cavity where if forms part of the floor and lateral walls, the oral cavity in which it forms the rearmost 25% of the roof of the mouth (the other 75% being formed by the palatine processes of the maxilla) and a small section of the rear floor of the orbit of the eye. It also contributes to the formation of the pterygopalatine and pterygoid fossae and the inferior orbital fissure.
Palatine Bone Function
As part of the skeletal system, this bony structure provides a suitably strong framework for other tissues but its complex shape needs to be considered in detail in order to understand the various functions of each part. This is best done by studying the detailed anatomical features of the palatine bone with particular reference to the location of such features in relation to other bones and tissues of the skull.
Palatine Bone Anatomy
The palatine bone does not have a single specific function but is more a collection of many different functions united in a single structure. Each of these individual functions can be more easily comprehended by carrying out a detailed examination of the physical structure of the palatine bone. The anatomy of the palatine bone is most easily understood by considering the features of each specific part and relating them to their location in the body. The horizontal plate, which forms the lower part of the letter “L” can be regarded as being approximately of quadrilateral shape having two surfaces and four borders. The superior (upper) surface is concave from side to side and forms the rear floor of the nasal cavity. The inferior (underneath) surface is slightly concave and rough. This forms the rearmost 25% of the hard palate (roof of the mouth). Near the posterior edge of this surface, there is a transverse ridge for the attachment of the aponeurosis (fibrous tissue) to which are attached the tensor veli palatini (the muscles which tense and move the soft palate). The four borders of the horizontal plate may next be considered and the anterior border can be seen to be rough and serrated where it articulates with the palatine processes of the maxilla. The posterior border is free and is utilised for the attachment of the soft palate. At the end of this border nearest to its articulation with the opposing palatine bone, the horizontal plate becomes sharp and pointed and together the two bones form a projection known as the posterior nasal spine. This is the point of attachment for the musculus uvulae which is the muscle which moves the uvula (for those unfamiliar with anatomical terminology, the uvula is the small part of the soft palate which hangs down at the rear of the oral cavity). The lateral border is united with the lower edge of the vertical part and is grooved by the lower end of the pterygopalatine canal. The medial border is the thickest and is serrated along the edge which articulates with the opposite palatine bone. The upper side of this edge raises up to form a ridge which, along with the other palatine bone, forms the nasal crest which is the point of articulation with the posterior part of the lower edge of the vomer (the bone which forms the lower part of the nasal septum).
The vertical part is mainly a thin oblong-shaped structure with two surfaces and four borders. The internal, nasal, surface has clearly defined sections. The lower part has a broad shallow depression which forms part of the middle meatus. Above this is the conchal crest which is a marked horizontal ridge. This articulates with the inferior nasal concha. Above the conchal crest another shallow depression forms part of the middle meatus surmounted by the ethmoidal crest which is another horizontal ridge, less marked than the conchal crest. This articulates with the middle nasal concha. Above this is a narrow horizontal groove forming part of the superior meatus. The external, maxillary, surface is mainly of a very rough and irregular shape where it articulates with the nasal surface of the maxilla. The upper rear section is smooth where it plays a part in the formation of the pterygopalatine fossa and the frontal part is also smooth where it forms the posterior part of the medial wall of the the maxillary sinus. The posterior part of this surface features a deep vertical groove which, when articulated with the maxilla, forms the pterygopalatine canal through which pass the palatine vessels and the anterior palatine nerve. The anterior border of the vertical part is thin and irregular in shape. At a position opposite to the conchal crest is the maxillary process which is a pointed projecting lamina which forms the lower and back part of the opening of the maxillary sinus. The superior border supports the orbital process to the front and the sphenoidal process behind with the two processes being separated by the sphenopalatine notch which lies just below the under-surface of the body of the sphenoid. This foramen leads from the pterygopalatine fossa to the posterior part of the superior meatus in the nasal cavity and the superior nasal and nasopalatine nerves pass through it along with other sphenopalatine vessels. The posterior border shows a deep groove with serrated edges for articulation with the medial pterygoid plate of the sphenoid. The lower, inferior, border is fused with the edge of the horizontal plate and, immediately in front of the pyramidal process, is grooved by the lower end of the pterygopalatine canal.
In addition to the two main parts of the palatine bone, there are three distinctive processes, these being the pyramidal, orbital and sphenoidal processes. The pyramidal process projects rearwards and outwards from the junction of the vertical and horizontal parts and is easily recognised by its rough serrated articulation furrows forming an inverted “V” shape on each side of a smooth triangular area. This smooth area houses a small portion of the pterygoideus internus (which is one of the muscles of mastication). The rough furrows articulate with the pterygoid plates. The anterior part of the lateral surface is rough where it articulates with the tuberosity of the maxilla. At the base of the pyramidal process, close to its union with the horizontal plate, are the lesser palatine foramina which carry the middle and posterior palatine nerves. The orbital process is positioned at a higher level and in front of the sphenoidal process and connected to the vertical part by a constricted neck. It comprises of five surfaces enclosing an air cell. Three of the surfaces are articular and two are non-articular. The anterior (or maxillary) surface is rough and articulates with the maxilla. The posterior (or sphenoidal) surface includes the opening of the air cell (which connects with the sphenoidal sinus) and the margins of the opening are rough and serrated for articulation with the sphenoidal concha. The medial (or ethmoidal) surface articulates with the labyrinth of the ethmoid. The non-articulated surfaces of the orbital process are related to the formation of the orbit. The superior (or orbital) surface forms a small section of the rear floor of the orbit and the lateral surface is adjacent to it, separated by a rounded border which forms part of the inferior orbital fissure. The sphenoidal process is in the form of a thin plate, substantially smaller than, slightly below and to the rear of the orbital process and has three surfaces and two borders. The superior surface articulates with the root of the pterygoid process and the underside of the sphenoidal concha. Its medial border reaches as far as the ala (everted lip) of the vomer and it features a groove which forms part of the pharyngeal canal. The medial surface is smooth and concave and forms the lateral wall of the nasal cavity. The lateral surface features both articulated and non-articulated portions with articulations being with the medial pterygoid plate and non-articulated, forming a smooth part of the pterygopalatine fossa.
The orbital and sphenoidal processes are separated by the sphenopalatine notch which in some instances may have bone fully united above, forming a complete foramen or in other cases may remain partly open or develop as two or more foramina.
Palatine Bone Disorders
The palatine bones are generally well protected but can be damaged by traumatic injuries such as facial fractures. Like all bones, they may suffer from infections and cancers and birth defects may occasionally cause some abnormalities.