ports, through fibrous tissue, the upper jaw. The con- 

 cave region between the two lateral expansions of the 

 vomer articulates by strong fibrous tissue with the 

 medial surface of the palatine, holding it immovably to 



Mandibular Region. 



Hyomandibular. — Expanded posteriorly, and 

 slightly narrowed anteriorly where it ends bluntly; car- 

 tilage filled at its posterior and anterior edges; ar- 

 ticulates by fibrous tissue posteriorly with the extreme 

 lateral edge of the posterior portion of the prootic and 

 with the anteromedial edge of the pterotic, as well as 

 along the medial surface of the ventral shaft of the 

 pterotic. Dorsomedially the hyomandibular is firmly 

 held by fibrous tissue to the lateral edge of the prootic 

 shelf and its posterolateral wing. Anteriorly the hyo- 

 mandibular articulates along its dorsal edge by fibrous 

 tissue with the posteroventral end of the metapterygoid, 

 while its extreme anteroventral edge articulates through 

 cartilage and fibrous tissue to the fibrous tissue sheet 

 between the metapterygoid, symplectic, and preoper- 

 culum. In about the middle of its length the posterior 

 edge of the hyomandibular has a blunt process with a 

 concave head for articulation by fibrous tissue with the 

 head of the operculum. Just anterior to this articular 

 area, the hyomandibular bears an elongate groove along 

 its posterolateral surface into which the slender postero- 

 dorsal end of the preoperculum fits and is tightly held by 

 fibrous tissue. 



Quadrate. — Wide posteriorly, tapering anteriorly 

 to a knob for articulation with the articular in the lower 

 jaw, while from its posteroventral edge it possesses a 

 well-developed posteriorly directed process; cartilage fill- 

 ed at its posterior edge; articulates by interdigitation 

 dorsally with the ectopterygoid, and, to a lesser extent, 

 with the extreme ventral edge of the mesopterygoid; ar- 

 ticulates posteriorly through cartilage with the metap- 

 terygoid; at the indented region on its lower posterior 

 edge the quadrate articulates by fibrous tissue and some 

 interdigitation with the anterior end of the symplectic, 

 which broadly overlies its lateral surface. Along most of 

 its ventral edge the quadrate articulates by fibrous tis- 

 sue with the preoperculum. 



Metapterygoid. — A more or less elongate, rec- 

 tangular plate, somewhat wider anteriorly than pos- 

 teriorly; cartilage filled at its anterior edge; articulates 

 anterodorsally by interdigitation with the mesoptery- 

 goid, which it broadly overlies; articulates anteroven- 

 trally through cartilage with the quadrate, while along 

 the anterior half of its ventral edge it articulates by inter- 

 digitation with the symplectic. The posterior and 

 posteroventral edges of the metapterygoid are firmly held 

 by fibrous tissue to the anterodorsal edge of the hyoman- 

 dibular. The dorsal end of the interhyal articulates by 

 fibrous tissue with the ventral edge of the metapterygoid 



just posterior to the posterodorsal end of the symplectic 

 and just in front of a ventral process of the metaptery- 

 goid. 



Symplectic. — Slender and somewhat triangular in 

 shape; slightly filled with cartilage at its anterior and, to 

 a lesser extent, posterodorsal end; articulates by fibrous 

 tissue and interdigitation anteriorly with the quadrate, 

 which it broadly overlies, and posterodorsally by fibrous 

 tissue and extensive interdigitation with the anteroven- 

 tral surface of the metapterygoid, which it also overlies. 

 The posterior edge of the symplectic is in contact with 

 the fibrous tissue sheet between the symplectic, metap- 

 terygoid, hyomandibular, and preoperculum, and its 

 posterodorsal end is closely adjacent to the region where 

 the dorsal end of the interhyal articulates with the 

 metapterygoid. 



Palato-Pterygoid Region. 



Palatine. — A sturdy dome; articulates by exten- 

 sive interdigitation ventrally with the ectopterygoid and 

 mesopterygoid. Dorsomedially the palatine articulates 

 by fibrous tissue with the concave region on the lateral 

 surface of the vomer between the two laterally expanded 

 processes of the vomer. 



Ectopterygoid. — Elongate, slightly widest in the 

 middle; articulates by extensive interdigitation dorsally 

 with the palatine, posteriorly with the mesopterygoid, 

 and ventrally with the quadrate, which broadly overlies 

 its posteroventral region. 



Mesopterygoid. — A large triangular slab whose 

 lateral surface is broadly overlain by the metapterygoid, 

 to which it is extensively interdigitated; anteriorly the 

 mesopterygoid extensively interdigitates with the 

 palatine and ectopterygoid and, to a much lesser extent, 

 with the upper posterior edge of the quadrate. 



Opercular Region. 



Operculum. — A relatively flat plate except at its 

 upper end where it is expanded into a facet for ar- 

 ticulation by fibrous tissue with the slight concavity on 

 the ventrally directed knob of the posterior edge of the 

 hyomandibular. Ventrally the operculum broadly over- 

 lies and articulates by fibrous tissue with the suboper- 

 culum. 



Suboperculura. — A thin plate, widest anteriorly, its 

 ventral region broadly rounded, 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. 



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