parasphenoid is concave and receives the rounded ven- 

 tral edge of the platelike portion of the ethmoid, to which 

 it articulates by fibrous tissue. The anterior end of the 

 parasphenoid is deeply concave to receive the posterior 

 shaftlike portion of the vomer, to which it is held by 

 fibrous tissue. 



Pterosphenoid. — Cartilage filled along all of its 

 lateral edges of articulation with the other cranial bones; 

 articulates through cartilage and fibrous tissue with the 

 frontal, which broadly overlies it, and through cartilage 

 and interdigitation with the sphenotic and prootic. Me- 

 dially the pterosphenoid possesses a projection toward 

 the midline which interdigitates with a similar projection 

 from its opposite member, the pterosphenoids here 

 meeting in the midline. The pterosphenoids also are iri 

 contact through cartilage at their extreme dorsomedial 

 ends. 



Ethmoid Region. 



Ethmoid. —Elongate and deep; expanded laterally 

 along its dorsal region but a deep flattened plate ventral- 

 ly, the rounded edge of the ventral plate fitting into a 

 concavity along the dorsal surface of the anterior end of 

 the parasphenoid and held there by fibrous tissue. More 

 anteriorly the ventral edge of the ethmoid articulates by 

 fibrous tissue and light interdigitation with the dorsal 

 surface of the anterior half of the vomer. Postero- 

 laterally the dorsal surface of the ethmoid is overlain and 

 interdigitated to the extreme anterior ends of the fron- 

 tals. Posteriorly the ethmoid articulates through its car- 

 tilage filled posterior edge with the anteroventral car- 

 tilaginous ends of the prefrontals. The anterior end of the 

 ethmoid is somewhat more laterally expanded than is the 

 dorsal edge behind it, especially ventrally where a flange 

 protrudes anteroventrally and articulates through 

 fibrous tissue with the posterior end of the palatine. The 

 extreme anterior end of the ethmoid remains somewhat 

 cartilaginous centrally, and it is against this cartila- 

 ginous face that the rear edge of the premaxillary abuts 

 in rotation. 



Vomer. — An elongate shaft except anteriorly where 

 it is laterally expanded; articulates posteriorly at its 

 shaftlike portion by fibrous tissue to the concavity at the 

 anterior end of the parasphenoid; articulates by fibrous 

 tissue and slight interdigitation dorsally with the antero- 

 ventral end of the ethmoid, while anteriorly it helps sup- 

 port the posterior end of the upper jaw. 



Mandibular Region. 



Hyomandibular. — A flat shaft for most of its 

 length, somewhat expanded dorsally; cartilage filled 

 anteroventrally; the posterior edge thickened for articu- 

 lation by fibrous tissue with the preoperculum and, just 

 above the dorsal end of the latter, with the anterodorsal 

 head of the operculum; articulates by fibrous tissue dor- 

 sally with the groove on the ventral surfaces of the 



prootic and pterotic, while posterodorsally the hyoman- 

 dibular abuts against and is firmly held by fibrous tissue 

 along the medial surface of the elongate portion of the 

 ventral flange of the pterotic. The articulation with the 

 head of the operculum is at a slight bulge of the hyo- 

 mandibular whose concave face is cartilage filled and 

 abuts against the similarly cartilage filled head of the 

 operculum. The anteroventral end of the hyomandib- 

 ular articulates variously through cartilage and fibrous 

 tissue with the posterior end of the metapterygoid, 

 symplectic, interhyal, and preoperculum. 



Quadrate. — Widest posteriorly, tapering to a knob 

 anteriorly for articulation with the articular in the lower 

 jaw; cartilage filled at its posterior edge; deeply cleft 

 along its posterior edge to accommodate the anterior end 

 of the symplectic; articulates dorsally by extensive inter- 

 digitation with the ectopterygoid, while posteriorly it ar- 

 ticulates through cartilage with the mesopterygoid and 

 metapterygoid; articulates by fibrous tissue and inter- 

 digitation with the symplectic. Ventrally the quadrate 

 articulates by fibrous tissue with the preoperculum. 



Metapterygoid. —A large flat plate curving 

 medially along its dorsal edge; cartilage filled at its 

 anterior and posterior edges; articulates anteriorly 

 through cartilage with the quadrate while anterodor- 

 sally it is overlain and interdigitated with the 

 mesopterygoid and anteroventrally extensively inter- 

 digitated with the symplectic. Along the middle of its 

 ventral edge it articulates through fibrous tissue with the 

 dorsal end of the interhyal. Posteroventrally the 

 metapterygoid articulates through fibrous tissue and car- 

 tilage with the preoperculum and anteroventral edge of 

 the hyomandibular. 



Symplectic. — A flattened shaft; relatively large; 

 cartilage filled at its posterior and, to a lesser extent, 

 anterior edges; articulates by extensive interdigitation 

 posterodorsally with the metapterygoid and anteriorly 

 with the indented region of the quadrate; ventrally ar- 

 ticulates by fibrous tissue and, in some cases, by slight 

 interdigitation with the dorsal edge of the preoperculum. 

 The posterior cartilaginous end of the symplectic is in 

 contact with the region of articulation between the in- 

 terhyal and metapterygoid. 



Palato-Pterygoid Region. 



Palatine. —A more or less simple short rod with a 

 slight bulge along its ventral edge for articulation by 

 fibrous tissue with the extreme anterodorsal edge of the 

 ectopterygoid; articulates anteriorly by fibrous tissue 

 with the dorsal head of the maxillary and posteriorly 

 with the lateral flanges of the ethmoid and, to a lesser ex- 

 tent, with the anterolateral expansion of the vomer. 



Ectopterygoid. —Elongate; more or less triangular, 

 the apex of the triangle being anterior in the middle of its 

 length where the ectopterygoid articulates through 



