Functional morphology of the pterygoid hamulus.

The pterygoid hamulus (PH), a structure on the under surface of the skull base which has so far hardly been described, is in a peculiar situation biomechanically. The aim of this study is to accumulate sufficient morphological data to enable a functional interpretation to be provided. A total of 93 adult skulls and 24 children's skulls have been examined, and also an additional 20 heads in which the relationship to the surrounding muscles could be investigated. Measurements were made with a sliding gauge, and sections cut from specimens embedded in methyl methacrylate were examined histologically. The hamulus is a variable structure which can, however, be allotted to one of a few basic types. As nomenclature we suggest the following terms: the base: Basis; body: Corpus, sulcus: Sulcus; neck: Collum; head: Caput of the hamulus. The average measurements are: length 7.2 mm, sagittal breadth 1.4 mm, transverse breadth 2.3 mm. The sections show that the medial cortical lamella is thicker than the lateral, and that the 2 are bound together by oblique trabeculae. The medial gradient angle of the collagen fibers is smaller than that of the lateral. A few muscles take origin from the hamulus, the tensor veli palatini turns round the neck, and a few of its fibers take origin here. The distribution of the material within the hamulus suggests that its body is subjected to greater loading in the medio-dorsal direction, but that the head is freely pulled away laterally and caudally. Its exposed position at the distal end of the upper dental arch and the formation of a bursa or sliding layer in the sulcus suggest that it may be a potential source of irritation.