92 ILLINOIS BIOLOGICAL MONOGRAPHS [92 



The palatines. These bones retain the same shape and relations as in the 

 younger stages, although now much larger in size (Fig. 15). Ossification has 

 proceeded in all parts and there is only a core of cartilage left. Each palatine 

 is a slender dumb-bell shaped ossification lateral to and below the ectethmoid 

 process with which it has articulated from its earliest stage. The anterior 

 ventral end is grooved for the articulation with the maxillary, and the pre- 

 maxillary is attached to these two bones by tough connective tissue. As 

 earlier, so now, the palatine has no actual contact with the pterygoquadrate 

 ossification. In Salmo the bone is continuous posteriorly with the bones of the 

 pterygoid arch and bears teeth on its ventral surface. In the Characinidae, 

 the palatine bone has varying sizes and shapes, but it is developed on cartilage 

 continuous posteriorly with the cartilage within the pterygoid bones. In 

 Erythrinus, the maxillary articulates with the palatine in the same manner as 

 in Amiurus, but the palatine does not extend as far forward. In Scomber 

 (Allis, 1903), the palatine is fused with the anterior bone of the pterygoid 

 series and bears teeth. 



The ectopterygoid. This bone develops by the ossification of a sheet of 

 connective tissue ventral to the palatine and connected with it by connective 

 tissue (Fig. 15). The posterior margin interdigitates with the anterior margin 

 of the large metapterygoid. McMurrich (1884b) described this bone as 'num- 

 ber four' and stated that it could not be homologized with a pterygoid bone 

 because it was developed from membrane. Schleip (1903) found that it 

 developed from membrane in Salmo and that it is separated from the pterygoid 

 cartilage by connective tissue and yet maintains that it is the homologue of the 

 ectopterygoid of other teleosts. The bone is very small, quadrate in outline, 

 mth delicate sculptured radiating lines. In Salmo it is longer and thinner 

 than in Amiurus and has more of the character of the corresponding bone in 

 Amia (Van Wijhe, 1882), the Characinidae and the Cyprinidae. There is 

 no entopterygoid in Amiurus. 



The metapterygoid. This large bone is developed around the pterygoid 

 part of the pterygoquadrate cartilage. It is quadrangular in outlme and inter- 

 digitates anteriorly with the ectopterygoid, posteriorly with the hyomandibu- 

 lar and ventrally with the quadrate (Fig. 15). No cartilage persists in any of 

 the visible parts of the bone. Medially it is attached to the lateral surface 

 of the cranium by a sheet of muscular and ligamentous tissue. A mesoptery- 

 goid occurs in most teleosts between the meta- and ectopterygoids, but in 

 Amiurus the two interdigitate. In Scomber a small strip of cartilage inter- 

 venes between the metapterygoid and the quadrate and there is a space 

 between the former and the elongate hyomandibular bone. In Salmo (Parker, 

 1873) the bone is not nearly as great in extent, occupies a position entirely 

 dorsal to the quadrate and is separated from the latter, as in Scomber, by 

 cartilage. It does not interdigitate with, but overlaps the hyomandibular. 



