its posteroventral region; articulates by fibrous tissue 

 dorsally with the ectopterygoid, ventrally with the 

 preoperculum, and anteriorly with the articular. 

 Posteriorly the quadrate articulates through cartilage 

 with the metapterygoid and symplectic. 



Metapterygoid. — Broad anteriorly, narrowing pos- 

 teriorly; cartilage filled along its anterior and ventral 

 edges; articulates through cartilage anteriorly with the 

 quadrate, ventrally with the symplectic, and posteriorly 

 with the cartilaginous area in front of the anterior end of 

 the hyomandibular. Dorsally the metapterygoid ar- 

 ticulates by fibrous tissue with the mesopterygoid. 



Symplectic. —Long and rod-shaped; cartilage filled 

 at its anterior and posterior ends; articulates through 

 cartilage anteriorly with the quadrate, dorsally with the 

 metapterygoid, posteriorly with the cartilaginous area in 

 front of the anterior end of the hyomandibular. Ven- 

 trally the symplectic articulates by fibrous tissue with 

 the preoperculum. 



Palato-Pterygoid Region. 



Palatine. — Cartilage filled at its anterior and pos- 

 terior ends; articulates by fibrous tissue anteriorly with 

 the dorsolateral surface of the maxillary, medially with 

 the lateral surface of the expanded portion of the vomer, 

 posteriorly with the mesopterygoid. A posterodorsal pro- 

 jection from its dorsal edge articulates by fibrous tissue 

 with the base of the ventrolateral surface of the pre- 

 frontal, and also connects to a band of fibrous tissue that 

 runs over and above the premaxillary pedicels to join 

 with the posterodorsal wing of the palatine on the other 

 side. The palatine is firmly held in place by these fibrous 

 tissue articulations even though it is not sutured to any 

 of the surrounding bones, 



Ectopterygoid. — Somewhat triangular in shape; ar- 

 ticulates closely by fibrous tissue along its ventral edge 

 with the quadrate, while along its posterodorsal edge it 

 articulates through a sheet of fibrous tissue with the 

 palatine and mesopterygoid. 



Mesopterygoid. — Relatively well developed, only 

 slightly smaller than the metapterygoid; articulates by 

 fibrous tissue anterodorsally with the palatine, antero- 

 ventrally with the ectopterygoid, and ventrally with the 

 metapterygoid. 



Opercular Region. 



Operculum. — Thin and broad ventrally, nar- 

 rowing to a stout shaft dorsally; articulates by fibrous tis- 

 sue dorsally with a groove on the upper posterior edge of 

 the hyomandibular. Ventrally the operculum slightly 

 overlies and is held by fibrous tissue to the suboper- 

 culum. 



Suboperculu 



-Rounded anteriorly, tapering to 



a point posteriorly; with a small dorsal projection located 

 in about the middle of its dorsal edge; articulates by fi- 

 brous tissue dorsally with the operculum, and anteriorly 

 with the interoperculum. 



Interoperculum. — Very elongate; wide and rounded 

 posteriorly but tapering to a point anteriorly; articulates 

 by fibrous tissue posteriorly with the suboperculum, 

 while anteriorly it makes a ligamentous attachment 

 to the angular in the lower jaw. In the posterior half 

 of its length the dorsal edge of the interoperculum con- 

 nects by a band of fibrous tissue to the epihyal in the 

 region where the epihyal articulates with the interhyal. 



Preoperculum. — Slightly expanded posteroven- 

 trally; the dorsal edge along the anterior half of the bone 

 slightly expanded laterally for articulation with the 

 quadrate; articulates by fibrous tissue along the pos- 

 terior region of its dorsal edge with the hyomandibular, 

 along the middle region of its dorsal edge with the car- 

 tilaginous plate between the symplectic, metaptery- 

 goid, hyomandibular, and quadrate, along the anterior 

 region of its dorsal edge with the quadrate. 



Upper Jaw. 



Premaxillary. — L-shaped, with the long posterior 

 arm (pedicel) movably articulated by fibrous tissue 

 along the dorsal surface of the vomer and ethmoid, allow- 

 ing for protraction of the upper jaw. When fully retracted 

 the pedicel reaches most of the way along the dorsal sur- 

 face of the ethmoid, almost to the tip of the frontals. The 

 shorter ventral arm of the premaxillary forms the an- 

 terior edge of the upper jaw, except for a short distance 

 ventrally where the maxillary forms the border. The pre- 

 maxillary articulates by fibrous tissue along the middle 

 of the lateral surface of its posterior arm with the medial 

 surface of the upper exptmded portion of the maxillary, 

 while along the medial surface of its posterior arm the 

 premaxillary articulates with its opposite member. The 

 ventral arm of the premaxillary articulates by fibrous tis- 

 sue along its posterior edge with the anterior edge of the 

 maxillary. Six to seven bluntly conical teeth, decreasing 

 in size laterally, are borne in deep sockets along the an- 

 terior edge of the premaxillary. Behind and internal to 

 this outer row of teeth there is usually a single conical 

 tooth, about half the size of the largest tooth in the outer 

 series, but several such inner teeth may be present on 

 each premaxillary. The teeth are replaced by new ones 

 developing in new sockets just above and external to the 

 sockets of the outer row of teeth. After a new tooth erupts 

 through the surface of the premaxillary, it gradually 

 migrates slightly forward and downward into the area of 

 the socket of the older tooth which it is replacing. 



Maxillary. — Rounded dorsally, constricted in the 

 middle, and only slightly expanded ventrally; ar- 

 ticulates by fibrous tissue dorsally along the lateral sur- 

 face of its rounded portion with the anterior end of the 

 palatine, while along the medial surface of its rounded 



