The pleurapophyses (palate bones) articulate above with the ossa plana of the ethmoid, or the neurapophyses of their own vertebral segment. Projecting downwards, they terminate in a rough tuberosity, which articulates with the haemapo-physes, or the superior maxillary bones. The pre-maxillaries represent the divided haemal spine. In cases of hare-lip, these distinct elements may be seen projecting forwards, with the incisor teeth, unconnected with the maxillary bones; the flat horizontally projecting palate plates articulate in the mesial line, and, from the forward direction of the haemal arch (maxillaries), are brought into contact with the under surface of the nasal centrum (Vomer), which is prolonged forwards to constitute a septum, which divides the nares into two cavities.
The pleurapophysial appendage (pterygoid process) is coalesced with the basi-sphenoid, and for this reason the upper jaw is not movable as in birds; it is firmly fixed to the base of the cranium, by the ossification of the pterygoid appendages to the basi-sphenoid. The tuberosity of the compressed palate-bone (pleurapophysis) articulates in front with the maxillaries (haemapophysis), and behind with its own appendage (pterygoid). The confluence of the latter with the basi-sphenoid binds all these bones to the base of the skull, and renders the upper jaw immovable. In birds, the elongated palate-bones alone support their own pterygoid appendages, which lie by the sides of the basi-sphenoid, but wholly unconnected with them; the upper maxilla, therefore, may be pushed upwards, and the pterygoid appendages moved from the central position, by the mechanical pressure of the ossa communi-cantia (malar and squamous bones).
The haemapophysial appendages (malar and squamous bones) extend from the rough tuberosity on the outer surface of the maxilla to the tympanic and mastoid bones (elements of the temporal). Nowhere is the adaptation of type to special purposes better seen than in the changes of form which these haemapophysial appendages undergo in the vertebrate subkingdom. Broad and expanded in the turtle, they articulate with the post-frontals, the mastoid, and the tympanic bones, to form the arch which covers in the temporal fossa. Slender and styliform in birds, they extend as the ossa com-municantia from the tympanic bones to the upper jaw, which is by their pressure elevated when the mandible is depressed. They are broad and expanded in man, but for a different purpose than in the turtle; the malar bone articulates with the post-frontal, and forms part of the outer wall of the orbit, and it sends inwards a process which, uniting with the alisphenoids, completes the anterior boundary of the temporal fossa.