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QUADRATE. 



The quadrate is a quadrant-shaped bone with its ventral corner thickened to form an artic- 

 ular surface for the mandible. The dorsal edge of the bone is wavy, and is bounded by cartilage 

 which separates it from the ventral edge of the metapterygoid. Its anterior edge is nearly straight, 

 is bevelled on its internal surface, and overlaps and fits against the external surface of the ventral 

 limb of the ectopterygoid. Its posterior edge is slightly convex, is thickened and grooved, and fits 

 against the anterior edge of the ventral portion of the preopercular. This thick posterior edge of the 

 bone terminates dorsally in a short point, usually longer and sharper than in the specimen used for 

 the figures. This point fits against the inner surface of a thin flange on the anterior edge of the 

 preopercular, and between it and the dorsal edge of the body of the quadrate there is a curved notch. 

 This notch forms the relatively wide dorsal end of a shallow and tapering groove on the inner sur- 

 face of the bone, the groove running downward and forward to the thickened articular head of the 

 bone, where it ends in a slight recess. The groove lodges the ventral three-fifths of the symplectic 

 and may be said to separate the quadrate into two parts, a body and a posterior process. The groove 

 is everywhere wider than that part of the symplectic that lies in it, a Channel thus being left on either 

 side of the latter element. At the upper end of the channel that lies anterior to the symplectic, there 

 is a perforation of the apparatus, through which the mandibularis internus facialis passes from the 

 outer to the inner surface of the palato-quadrate, and then runs downward in the channel along the 

 inner surface of the apparatus. At the upper end of the channel that lies posterior to the symplectic, 

 the mandibularis externus facialis passes, in a similar manner, from the outer to the inner surface 

 of the apparatus, the arteria hyoidea traversing the same opening. 



The posterior process of the quadrate of fishes is a feature of some morphological importance. 

 It is not found, as a part of the quadrate, in the bony ganoids, but is found in most, if not all teleosts. 

 It probably is present in all the Acanthopterygii and Anacanthini, for it is shown in all the figures 

 that I can find of the quadrate of those fishes. In Siphonostoma, of the Lophobranchii, it would 

 seem to be certainly present, though Supino's figure ('06) is not very definite in this particular. In 

 Balistes, of the Plectognathi, I find it in normal position, and it is shown by Brühl ('56) both in this 

 fish and in Diodon. Among the Physostomi, of Günther's Classification, it is shown in Belone 

 (Swinnerton, '02), Esox (Swinnerton, '02), Galaxias (Swinnerton, '03), Salmo (Parker, '73), Hyodon 

 (Ridewood, '04 b), Osteoglossum (Ridewood, '05 a), Megalops (Ridewood, '04 a), Alepocephalus 

 (Gegenbaur, '78) and Notopterus (Ridewood, '04 b). In Ameiurus (Mc Murrich, '84), Silurus (Jaquet, 

 '98) and Erythrinus (Sagemehl, '84 b) it seems to be present, in a modified form, as a short process 

 that gives support to the lower end of the preopercular. In Carassius auratus, I find it as a short 

 but normal process, a short groove here lodging a short terminal portion of the symplectic. In 

 Ridewood's figures of the Mormyridae ('04 b) it seems to be wholly absent, as it does also in most 

 of that author's figures of the Clupeoid fishes ('04 c); but Erdl ('47) apparently shows it in Gym- 

 narchus, and I find it perfectly normal, though small, in Clupea harengus. In the Muraenidae, which 

 I am investigating, I am of the opinion that both this process and the symplectic are indistinguishably 

 fused with the quadrate, and it may be that this same fusion has taken place in other fishes where 

 these two structures seem to be wanting. In Erythrinus Sagemehl says ('84 b, p. 92) that the sym- 

 plectic and quadrate are so closely united that even the lines separating the bones are nearly lost, 

 this evidently representing a stage in the complete fusion of these bones. 



