Ectoptcrygoid. —Elongate; articulates by inter- 

 digitation dorsally with the palatine, posteriorly with the 

 mesopterygoid, which it somewhat overlies, and ven- 

 trally with the quadrate, which it also overlies. 



Mesopterygoid. —Large; articulates by inter- 

 digitation posteroventrally with the metapterygoid, 

 while anteriorly it interdigitates with and is somewhat 

 overlain by the palatine, ectopterygoid, and quadrate. 



Opercular Region. 



Operculum. —Relatively short and thin; more or 

 less rounded in outline, with a protuberance dorso- 

 medially for articulation by fibrous tissue with a slight 

 concavity on the ventral edge of the hyomandibular. 

 Ventrally the operculum broadly overlies and ar- 

 ticulates by fibrous tissue with the suboperculum. 



Suboperculum. —Very thin; widest in the middle, 

 broadly rounded anteriorly, tapering to a point pos- 

 teriorly; articulates by fibrous tissue dorsally with the 

 broadly overlying operculum. At the anterior edge of the 

 region where the operculum overlies the suboperculum, a 

 strong ligament coming from the interoperculum makes 

 contact with the suboperculum and, to a lesser extent, 

 with the operculum. 



Interoperculum. — A short rod; extends from the 

 level of the anterior end of the preoperculum to the level 

 of the junction of the ceratohyal and epihyal; connects by 

 a strong ligament anteriorly to the angular in the lower 

 jaw, while posteriorly it connects by a short ligament to 

 the epihyal and by a longer more diffuse ligament to the 

 anterior edge of the suboperculum and, to a lesser ex- 

 tent, of the operculum. 



Preoperculum. — Relatively short; not much ex- 

 panded in its middle region, and tapering to narrow ends 

 anteriorly and posteriorly; articulates by fibrous tissue 

 anteriorly along its dorsal edge with the quadrate and, to 

 a slight extent, with the symplectic; posteriorly the nar- 

 row shaft of the preoperculum is held by fibrous tissue in 

 an elongate concavity on the lower lateral surface of the 

 hyomandibular. 



Upper Jaw. 



Premaxillary. — A slightly curved plate, wider dor- 

 sally than ventrally; its posterodorsal region somewhat 

 concave for articulation by fibrous tissue with the an- 

 terior edges of the vomer and ethmoid; the anterior edge 

 of the upper jaw formed by the premaxillary, except for a 

 short distance ventrally where it is formed by the maxil- 

 lary; the dorsomedial edges of the two premaxillaries 

 held in close apposition by fibrous tissue. Each pre- 

 maxillary in adults usually bears five or six teeth in a 

 single row. The teeth are borne in relatively deep and 

 elongate grooves on the outer surface of the premaxil- 

 lary. The lowermost teeth are shaftlike and taper to 



sharp points, but more dorsally and medially they are 

 flattened and blunter at their distal ends. At the pos- 

 terior end of each tooth-bearing groove there is a deep 

 socket in which new teeth develop before moving for- 

 ward to replace the old ones. Most of the interior of the 

 premaxillary contains the dental pulp from which the 

 new teeth develop. This pulp cavity communicates with 

 the exterior not only by the deep sockets in which the 

 new teeth develop but also by a large hole in the postero- 

 dorsal surface of the premaxillary. The premaxillary ar- 

 ticulates by extensive interdigitation with the maxillary 

 along all of its posterior edge, except for a short distance 

 dorsally. 



Maxillary. — Widest ventrally, constricted in the 

 middle of its length; articulates by extensive interdigita- 

 tion anteriorly along all of its length with the pre- 

 maxillary, which it somewhat overlies. The maxillary ar- 

 ticulates by fibrous tissue posterodorsally with the 

 anterior edges of the vomer and ethmoid and ventro- 

 medially with the dorsolateral surface of the dentary. 



Lower Jaw. 



Dentary. — Wider posteriorly than anteriorly; its 

 posteromedial surface concave dorsally to accommodate 

 the articular, with which it interdigitates. Just below the 

 articular, the dentary interdigitates with the angular. 

 The ventromedial edges of the two dentaries are held 

 closely together by fibrous tissue. Laterally from its 

 posterodorsal region the dentary articulates by fibrous 

 tissue with the medial surface of the maxillary. Each 

 dentary in adults usually bears four or five teeth, like 

 those of the upper jaw, in deep grooves on its outer sur- 

 face, each of the tooth-bearing grooves ending pos- 

 teriorly in a deep socket in which new teeth develop. The 

 sockets are in communication with the large pulp cavity 

 that fills most of the hollow interior of the dentary. The 

 pulp cavity communicates with the exterior not only at 

 the tooth sockets but also at its posterior concave region 

 of articulation with the articular. 



Articular. — Small; its posterior edge with a con- 

 cavity for articulation by fibrous tissue with the anterior 

 knoblike process of the quadrate. Anteriorly the articular 

 interdigitates with the concave upper half of the postero- 

 medial surface of the dentary. On the medial side of its 

 ventral edge the articular interdigitates with the angular, 

 but the lateral surfaces of these two bones are not in con- 

 tact; rather, they are slightly separated by the dentary. 

 The sesamoid articular is a roundish nubbin of bone 

 closely held to the medial surface of the articular just 

 behind the region where the upper medial edge of the ar- 

 ticular meets the medial surface of the dentary. 



Angular. —Small, slightly elongate; articulates by 

 interdigitation dorsomedially with the articular, while 

 dorsolaterally, anteriorly, and ventrally it interdigitates 

 with the dentary. Posteriorly the angular connects by 

 ligament with the anterior end of the interoperculum. 



