In tetrapods, the pterygoid is a complex, but relatively stable, paired palatal bone with a number of parts. For the following discussion, it may be best to refer to the images of tetrapod palates at, for example Ornithosuchus, Therapsida, or Palatines. In many tetrapods, it is the largest palatal bone and serves as the main structural support. Most typically, the pterygoids meet extensively on the mid-line of the palate and jointly send a process, the palatal ramus, anteriorly, which may cover the parasphenoid more or less completely. Sometimes this term is used to include the main body of the pterygoid as well. More variably, there are one or two anterolateral processes which go by various names, such as ectopterygoid ramus. In many amniotes, the pterygoid develops a strong transverse process or transverse flange which forms a bar running laterally across the palate. The pterygoid also articulates with (where present) the dorsoventral supports for the palate: the epipterygoid (dorsal) and the basipterygoid process of the braincase. Finally, the pterygoid sends a long, robust quadrate ramus with complex curvature down (posteroventrally) to grasp the quadrate and support the jaw articulation. Basally, in fishes, the terminology tends to be a little different. Refer to the image of the Frasnian actinistian Diplocercides. The pterygoid bone of tetrapods is, roughly speaking, derived from the middle, entopterygoid (see also entry at entopterygoid for alternative definitions) portion of the palatoquadrate complex. The entopterygoid is not actually a part of the palatoquadrate. It is a dermal bone which has replaced the middle section of the primitively continuous endochondral bone of the palatoquadrate, the original upper jaw. In tetrapods, the pterygoid advances further, and also replaces the central part of the posterior, pterygoquadrate unit. This becomes the quadrate ramus. The upper part of this unit, the portion involved in the dorsal and basipterygoid articulations between jaw and braincase, is referred to as the metapterygoid. In tetrapods, most of this region is incorporated into the pterygoid as well, with the exception of the ascending process of the palatoquadrate, which becomes the epipterygoid. Since the anterior braincase articulation is lost in tetrapods, the only remaining sections of the palatoquadrate are the epipterygoid and the quadrate (or, in mammals, the incus). Everything else is either lost or is replaced by the pterygoid[Palaeos], Palatal bones of intramembranous origin that lie anterior to the otic capsules, lateral to the orbits, and medial to the maxillae.[AAO]

Sources vary as to whether the pterygoid corresponds to the pterygoid processes in general, or the latter/inner plate.

inner plate of pterygoid process

pterygoid

uberon

UBERON:0010389

pterygoid bone, Lateral plate of pterygoid process

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