Orbital Region. 



Frontal. — A relatively flat plate; expanded pos- 

 terolaterally to overlie and articulate by fibrous tissue 

 with the supraoccipital, epiotic, and sphenotic. The 

 medial edges of the two frontals are broadly concave and 

 enclose between themselves the anterior portion of the 

 cartilaginous tissue of the otic and occipital regions. The 

 dorsomedial edges of the two frontals articulate with one 

 another by fibrous tissue. Along its posteroventral edge 

 the frontal overlies and articulates by fibrous tissue 

 with the pterosphenoid and sphenotic. Anteriorly the 

 rounded end of the frontal broadly overlies and artic- 

 ulates by fibrous tissue with the ethmoid and prefron- 

 tal. 



Prefrontal. — A more or less vertical column pos- 

 terolaterally, but expanded into a thin vertical sheet 

 anteriorly; cartilage filled along the middle region of its 

 medial surface; articulates by fibrous tissue posterodor- 

 sally with the overlying frontal, anteromedially with the 

 ethmoid, and anterolaterally with the palatine. A canal 

 for the olfactory nei-ve and vessels is present through the 

 substance of the prefrontal, rather than being present at 

 the interface of the prefrontal, frontal, and ethmoid car- 



Basisphenoid. — A large rounded plate anteriorly, 

 but laterally expanded posteriorly into a process whose 

 concave posterior surface articulates by fibrous tissue 

 with the medial edge of the anteroventral region of the 

 prootic. The ventral edge of the basisphenoid articulates 

 by fibrous tissue with the longitudinal concavity on the 

 dorsal surface of the parasphenoid. The anterior and dor- 

 sal edges of the upper half of the basisphenoid are carti- 

 lage filled. Dorsally the basisphenoid articulates by 

 fibrous tissue with the ventral edge of the ptero- 

 sphenoid. A small gap is present between the otherwise 

 closely apposed edges of the pterosphenoid and basi- 

 sphenoid which serves as a foramen for the exit of vessels 

 from the cranial cavity. 



Ethmoid Region. 



Ethmoid. — Thick and squarish; continuous pos- 

 teroventrally with the remains of the ethmoid cartilage; 

 articulates by fibrous tissue along the anterior half of its 

 ventral surface with the vomer and along the posterior 

 half of its ventral surface with the dorsal surface of the 

 concave anterior end of the parasphenoid. The lateral 

 surfaces of the ethmoid articulate by fibrous tissue ante- 

 riorly with the palatines and posteriorly with the pre- 

 frontals. 



Parasphenoid. — Elongate; expanded ventrally 

 along most of its length into a stout, but not particularly 

 deep, flange. About two-thirds the way back its length 

 the parasphenoid gives rise to a pair of short posterodor- 

 sally directed wings which articulate by fibrous tissue 

 with the anteroventral edges of the prootics. Posterior to 

 these dorsal wings, the parasphenoid articulates by fi- 

 brous tissue laterally with the posteromedial edges of the 

 prootics and posteriorly with the anteromedial surface of 

 the basioccipital. Just anterior to its dorsal wings, the 

 dorsal surface of the parasphenoid becomes concave for a 

 short distance to receive and hold by fibrous tissue the 

 ventral edge of the basisphenoid. Along the lateral sur- 

 face of about the anterior one-fourth of its length the 

 parasphenoid articulates by fibrous tissue with the thin 

 posterior portion of the palatine. The anterior end of the 

 parasphenoid is deeply concave and filled with gela- 

 tinous tissue. The posterior end of the vomer does not fit 

 into this concavity; rather, the ventral edge of the con- 

 cave anterior end of the parasphenoid supports by 

 fibrous tissue the posterior edge of the vomer. The dorsal 

 portion of the concave anterior edge of the parasphenoid 

 articulates by fibrous tissue with the ventral surface of 

 the ethmoid. 



Pterosphenoid. —A relatively flat plate; cartilage 

 filled along all of its edges, except medially; articulates 

 through cartilage posteroventrally with the prootic and 

 posterodorsally with the sphenotic. Dorsally the 

 pterosphenoid is overlain by the frontal, with which it ar- 

 ticulates by fibrous tissue. The ventral edge of the 

 pterosphenoid articulates by fibrous tissue with the dor- 

 sal edge of the basisphenoid. 



Vomer.— A small squarish bone articulated by 

 fibrous tissue dorsally with the anterior half of the ven- 

 tral surface of the ethmoid, laterally with the medial 

 edges of the palatines and posteriorly with the ventral 

 edge of the concave anterior end of the parasphenoid. 

 The anterior edges of both the vomer and ethmoid ar- 

 ticulate by fibrous tissue with the posteromedial edge of 

 the upper jaw. 



Mandibular Region. 



Hyomandibular. — Expanded posterodorsally, but 

 tapering anteroventrally to a thick rounded shaft; carti- 

 lage filled at its anteroventral edge and along the ante- 

 rior one-third of its dorsal edge. The hyomandibular ar- 

 ticulates by fibrous tissue along most of the length of its 

 dorsal edge with the ventrolateral surface of the pterotic, 

 but anterodorsally it is also supported by the medial por- 

 tion of the posteroventral edge of the sphenotic and by 

 the ventrolateral flange of the prootic. Along the ventral 

 half of its posterior edge the hyomandibular articulates 

 by fibrous tissue with the posterior half of the dorsal edge 

 of the preoperculum. Dorsally along its anteroventral end 

 the hyomandibular articulates by fibrous tissue with the 

 posteroventral edge of the metapterygoid. Just above the 

 posterodorsal end of the preoperculum, the hyomandi- 

 bular possesses a thickened area whose concave poste- 

 rior face articulates by fibrous tissue with the concave 

 anterior end of the operculum. 



Quadrate. — Wide posteriorly, but tapering to a 

 knob anteriorly for articulation with the articular in the 

 lower jaw; a short posteriorly directed process present 



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