edge; articulates by fibrous tissue ventrally with the 

 region of articulation between the vomer and para- 

 sphenoid; articulates at its dorsal surface by interdigi- 

 tation anteromedially with the ethmoid and postero- 

 medially and posteriorly with the frontal. Along most of 

 its medial surface it is attached to the ethmoid cartilage, 

 with which it is continuous. 



Parasphenoid. — Elongate, with a well-developed 

 ventral keel in the suborbital region. The anterior end of 

 the parasphenoid is deeply concave and into this con- 

 cavity the shaftlike posterior end of the vomer interdigi- 

 tates. The parasphenoid articulates laterally by fibrous 

 tissue with the base of the prefrontal in this region. Pos- 

 teriorly the parasphenoid slightly overlies the anterior 

 end of the basioccipital and strongly interdigitates with 

 it. About three-fourths the way back its length the para- 

 sphenoid gives rise to its paired dorsolateral wings that 

 interdigitate with the anteromedial edges of the prootics. 

 Posterior to this area of interdigitation with the antero- 

 medial edges of the prootics, the lateral edges of the 

 parasphenoid interdigitate with the ventromedial edges 

 of the prootics. In about the middle of its length the para- 

 sphenoid gives rise to an interorbital projection into 

 whose deeply concave dorsal surface the ventromedial 

 projections of the frontals interdigitate. 



Pterosphenoid. — A thin plate; cartilage filled along 

 its dorsal edge; articulates by interdigitation postero- 

 ventrally with the prootic and posterolaterally with the 

 sphenotic. For most of its length the pterosphenoid over- 

 lies the posteromedial portion of the ventral surface of 

 the frontal, and slightly interdigitates with it. 



ncave anterior end of the parasphenoid. Along the dor- 

 solateral surface of the vomer there is a laterally projec- 

 ting bony shelf above and below which fits the deeply 

 notched posterodorsal region of the palatine, the articu- 

 lation being by fibrous tissue. 



Mandibular Region. 



Hyomandibular. — Expanded dorsally, tapering to a 

 stout shaft anteroventrally; cartilage filled at its antero- 

 ventral and dorsal edges; articulates by fibrous tissue 

 dorsolaterally with the sphenotic and pterotic and dorso- 

 medially with the prootic and pterotic. Along the ventral 

 three-fourths of its posterior edge it articulates by fibrous 

 tissue with the preoperculum, while just above the dorsal 

 end of the latter the hyomandibular supports the articu- 

 lar face of the operculum. Anteriorly the hyomandibular 

 articulates by fibrous tissue principally with the pos- 

 terior region of the metapterygoid and symplectic. 



Quadrate. — Wide posteriorly, but tapering to a 

 knob anteriorly for articulation with the articular in the 

 lower jaw; a short, posteriorly directed process present 

 from its posteroventral edge; cartilage filled at its pos- 

 terior edge; articulates by fibrous tissue anteriorly with 

 the articular, anterodorsally by interdigitation with the 

 slightly overlying ectopterygoid, dorsally by interdigi- 

 tation with the broadly overlying mesopterygoid, and 

 ventrally by fibrous tissue with the preoperculum. 

 Posteriorly the quadrate articulates through cartilage 

 with the metapterygoid and symplectic, the anterior part 

 of the latter being overlain by the short posterior process 

 of the quadrate. 



Ethmoid Region. 



Ethmoid. — Large, more or less rectangular; articu- 

 lates by interdigitation posterodorsally with the overly- 

 ing frontals and posterolaterally with the prefrontals. 

 Along the anterior half of its ventral surface the ethmoid 

 articulates with the vomer, the posterior part of this ar- 

 ticular surface showing interdigitation, while more 

 anteriorly the two bones are completely fused. In small 

 specimens (under approximately 100 mm) it can be seen 

 that the anterior edge of the ethmoid region is actually 

 formed by the upturned anterior edge of the vomer, even 

 though in large specimens no such distinction can be 

 made. Anterolaterally the ethmoid articulates by fibrous 

 tissue with the palatine, although the main articulation 

 of the latter is with the vomer. In large specimens the 

 ethmoid tends to become swollen and porous, or hy- 

 perostotic. Just behind its articulation with the vomer, 

 the posteroventral surface of the ethmoid is continuous 

 with the remains of the ethmoid cartilage. 



Vomer. — Broad anteriorly, but tapering to a stout 

 shaft posteriorly; articulates with the ethmoid by fusion 

 anterodorsally but by interdigitation posterodorsally. 

 The posterior shaft of the vomer interdigitates with the 



Metapterygoid. — Broad anteriorly; cartilage filled 

 at its anterior edge; articulates through cartilage 

 anteriorly with the quadrate and ventrally with the 

 symplectic, the latter also slightly overlying and inter- 

 digitating with the metapterygoid. The metapterygoid 

 articulates by fibrous tissue posteroventrally with the 

 hyomandibular, preoperculum, and interhyal, while 

 anterodorsally it broadly overlies and slightly interdigi- 

 tates with the mesopterygoid. 



Symplectic. — Small, somewhat irregular in shape 

 from specimen to specimen; cartilage filled at its pos- 

 terior edge; articulates through cartilage and slight inter- 

 digitation anteriorly with the overlying process of the 

 quadrate and dorsally with the metapterygoid; articu- 

 lates by fibrous tissue posteroventrally with the preoper- 

 culum and interhyal. 



Palato-Pterygoid Region. 



Palatine. — Expanded posteriorly; a deep, ante- 

 riorly directed cleft present in its upper posterior edge 

 which fits tightly above and below the thin lateral 

 shelf of the vomer, articulating with it by fibrous tissue. 

 Anteroventrally the palatine interdigitates with the ec- 

 topterygoid, while posteriorly it overlies and interdigi- 



