. Bulletin of the British Museum (Natural History). Adductor mandibulae muscles (Fig. 1). The adductor is a single muscle mass originating on the preoperculum and metapterygoid. Anteriorly it inserts through a fairly well-developed and deep tendon onto the posterior margin of the compound angulo-retroarticular bone at about its mid- point. Ventral to this point of insertion there appears to be another, effected through an area of much looser connective tissue. On the medial face of the main adductor muscle mass the Acu portion arises from an extensive tendinous aponeurosis (Fig, 2). Muscle Au&
. Bulletin of the British Museum (Natural History). Adductor mandibulae muscles (Fig. 1). The adductor is a single muscle mass originating on the preoperculum and metapterygoid. Anteriorly it inserts through a fairly well-developed and deep tendon onto the posterior margin of the compound angulo-retroarticular bone at about its mid- point. Ventral to this point of insertion there appears to be another, effected through an area of much looser connective tissue. On the medial face of the main adductor muscle mass the Acu portion arises from an extensive tendinous aponeurosis (Fig, 2). Muscle Au> deepens as it runs forward so that it comes to occupy almost the entire Meckelian fossa, in which it has its insertion. Apart from the fact that no fibres of the adductor mandibulae are inserted onto the maxilla, this muscle in Pterothrissus closely resembles that of Elops saurus (see Vrba, 1968). The maxillo- mandibular ligaments of Pterothrissus, however, are quite different since there is no typical liga- mentum primordium in this genus. In Elops there is what can be considered a typical lower teleostean ligamentum primordium (see Winterbottom, 1974: 232), as well as a posterior liga- mentous connection between the maxilla and the lower jaw. I would interpret the latter as being homologous with the only ligaments present in Pterothrissus, which, therefore, does not have a true ligamentum 10mm Fig. 2 Pterothrissus belloci. Medial aspect of right lower jaw. Drawn by Miss E. Tarr; same specimen as in Fig. 1. Levator arcus palatini muscle. This is a moderately large muscle originating from the pterotic and sphenotic regions of the skull (Fig. 1). Its main body is subdivided, one set of fibres running obhquely backwards and downwards to insert medially on the metapterygoid. The other part of the muscle runs almost vertically downwards to insert dorso-anteriorly on the lateral face of the metapterygoid. Adductor arcus palatini muscle. A few fibres representing thi
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