Annals of the South African MuseumAnnale van die Suid-Afrikaanse Museum . R. C. Fig. 18. Diagram to illustrate the action of the lower jaw. and if y is increased the fibre orientation would become more posteriorlydirected. It is clear therefore that the coronoid process in terms of height (y)and distance from the articulation (x) is functionally important in determiningthe action of the lower jaws and its associated musculature, and not as DeWeerdt (1971) suggests, mainly a strengthening device. CRANIAL AND CERVICAL MUSCLES OF TYPHLOSAURUS AURANTIACUS AURANT1ACUS 209 The vertebrate lower jaw,

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Annals of the South African MuseumAnnale van die Suid-Afrikaanse Museum . R. C. Fig. 18. Diagram to illustrate the action of the lower jaw. and if y is increased the fibre orientation would become more posteriorlydirected. It is clear therefore that the coronoid process in terms of height (y)and distance from the articulation (x) is functionally important in determiningthe action of the lower jaws and its associated musculature, and not as DeWeerdt (1971) suggests, mainly a strengthening device. CRANIAL AND CERVICAL MUSCLES OF TYPHLOSAURUS AURANTIACUS AURANT1ACUS 209 The vertebrate lower jaw, seen in terms of the mechanics of a third classlever, would theoretically function at optimal efficiency with the adductorfibres orientated perpendicular to the long axis of the lower jaw and insertedon to the jaw as close as possible to the symphysis. Ostrom (1964) notes two disadvantages in this arrangement. As a resultof increasing x the gape of the mouth will correspondingly decrease. However,De Mar & Barghusen (1973: 626) state: If the increase in relative length

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Keywords: ., bookauthorsouthafr, bookcentury1800, bookdecade1890, bookyear1898