MANDIBULOHYOID CONNECTION IN CIRRHITOID FISHES 



97 



Fig. 3 Acantholatris monodactylus Medial aspect of left lower jaw, cheek region and hyoid arch. Scale = 2mm. 1: Anguloarticular-dentary 

 ligament; 2a: maxillary tendon of adductor mandibulae muscle A,; 2b: extension of above tendon joining tendinous aponeurosis of 

 adductor mandibulae muscle Aw; 3: tendon of Aw muscle to preoperculum; 4: epihyal-interopercular ligament; 5: tendon from Aw muscle 

 to interoperculum; 6: interopercular-mandibular ligament; 7: interhyal-quadrate-entopterygoid ligament. Dashed outline that of the 

 mandibulohyoid connection. 



muscle, whose insertion on the maxilla is identical with that in 

 the latter taxon. 



The Aw portion of the adductor mandibulae muscle in 

 Cheilodactylus is noticeably less extensive than in Acanthola- 

 tris, but its tendinous connections with the interoperculum 

 and the palatoquadrate arch are more complicated than in 

 that taxon. Also, in Cheilodactylus the ventral extension of 

 the adductor mandibulae A x maxillary tendon is noticeably 

 stouter than in Acantholatris (cf. Figs 3 & 4) but, unlike 

 Acantholatris , in Cheilodactylus it is derived from the medial 

 and not the lateral tendinous aponeurosis of the muscle's Aw 

 division. A most obvious difference between the two taxa is 

 the absence of a ligament connecting the hyoid arch with the 

 mandible in Cheilodactylus (cf. Figs 3 & 4). 



A somewhat tendinous section of the adductor mandibulae 



I Aw division (tendon 3 in Fig. 4) in Cheilodactylus runs 

 posteriorly, becoming completely tendinous as it crosses the 

 hind margin of the anguloarticular and its joint with the 

 quadrate. It inserts on the anterior tip of the preoperculum 

 just below that bone's dorsal margin. At a point near the 

 centre of the anguloarticular this partly tendinous section of 

 the Aw division of the adductor mandibulae muscle gives off 



I a ventroposteriorly directed branch which soon becomes 



, completely tendinous. The anterior part of this tendon (5a in 

 Fig. 4), immediately below its point of departure from tendon 

 3, is attached to the anguloarticular near its anterior margin. 

 It thus lies below the bone's articulation with the quadrate. 



I The posteriad extension of tendon 5a runs backwards and 

 somewhat dorsally, seemingly joining the lateral face of a 



, broad, stout, dense, and obliquely orientated ligament-like 

 strap (5b in Fig. 4) extending from the midpoint of the 

 quadrate to the anteroventral surface of the interoperculum. 

 Together the two elements (ie 5a and 5b in Fig. 4) form a 'Y' 

 shaped linkage between the anguloarticular, quadrate, and 



I interoperculum. Also, because the anterior arm of the 'Y' (ie 



5a) is associated with an extension of the Aw muscle onto the 

 anguloarticular, the linkage involves that bone as well. 



Without ontogenetic information it is difficult to decide 

 whether the element 5b of the 'Y' is, at it appears to be, a 

 branch of the tendon 5a (and thus is itself a tendon) or 

 whether it is strictly a ligament with which tendon 5a has 

 fused. That none of the other cirrhitoids examined has a 

 quadrato-interopercular ligament would add credence to 5b 

 being a true branch of 5a, and thus representing a consider- 

 able posterior extension of the Aw muscle's tendon system. 

 Also, in the other cheilodactylids examined, the 'Y'-shaped 

 connection gives no hint of it having originated from a tendon 

 and a ligament (see below). The potential complexity and 

 posterior extension of that system is clearly demonstrated in 

 another percomorph, the percid Gymnocephalus cernua (L.); 

 see Elshoud-Oldenhave & Osse (1976; fig. 4.1). 



When comparisons are made with the latrid Acantholatris, 

 (see p. 94 and Fig. 3) it appears that the 'Y'-shaped complex 

 in Cheilodactylus is, from its disposition and attachment 

 points, homologous with the simple tendon (5 in Fig. 3) 

 associated with the Aw portion of the adductor mandibulae 

 muscle in Acantholatris. Tendon 5 in that taxon is attached to 

 both the anguloarticular and the medial face of the interoper- 

 culum, and is separated by a short section of Aw from tendon 

 3 which inserts on the preoperculum (Fig. 3). In turn, and 

 also from its disposition and points of attachment, the latter 

 tendon would seem to be homologous with the longer tendon 

 3 in Cheilodactylus which also inserts on the preoperculum. 

 An early evolutionary stage in the development of this 

 complex in both Cheilodactylus and Acantholatris may be 

 represented by the tripartite posterior extension of the Aw 

 aponeurosis in Mendosoma, which also serves to link the Aw 

 muscle with the quadrate, preoperculum and interoperculum 

 (see p. 94 and Fig. 2). 



The two other cheilodactylid species dissected, Chirodacty- 



