Basisphenoid. — Laterally compressed throughout 

 its length, except posteriorly where it is laterally expand- 

 ed into a rounded process which articulates by fibrous 

 tissue with the anterior edge of the dorsal roof of the 

 myodome in the smaller specimen, while in the larger 

 specimen the posterior end is attached more dorsally to 

 the membranous wall between the two pterosphenoids. 

 From its posterior place of attachment to the prootics, 

 the basisphenoid is directed anteroventrally and ends in 

 the fibrous tissue sheet of the interorbital septum. This 

 anterior edge, which is slightly cartilage filled, is some 

 distance removed from the dorsal surface of the para- 

 sphenoid below it. 



culum and anteriorly with the symplectic and interhyal, 

 as well as with the slightly overlying posterior edge of the 

 metapterygoid. 



Quadrate. — Widest posteriorly, tapering to a knob 

 anteriorly for articulation by fibrous tissue with the ar- 

 ticular in the lower jaw; cartilage filled at its posterior 

 edge; prolonged from its posteroventral edge into a thin 

 process which articulates by fibrous tissue with the 

 symplectic; articulates by fibrous tissue anterodorsally 

 with the ectopterygoid, ventrally with the preoperculum, 

 posteriorly with the metapterygoid, and posterodorsally 

 with the mesopterygoid. 



Ethmoid Region. 



Ethmoid. —Large and wide; relatively thin in the 

 posterior half of its length, but becoming much deeper 

 anteriorly; the posterior half of its ventral surface 

 irregularly concave and continuous with the ethmoid car- 

 tilage; articulates posterodorsally by interdigitation with 

 the overlying frontals and posterolaterally through car- 

 tilage and interdigitation with the prefrontals. Antero- 

 laterally the ethmoid is extensively interdigitated with 

 the medial edges of the palatines. The medial region of 

 the anteroventral surface of the ethmoid is extensively 

 interdigitated with the dorsal surface of the vomer in the 

 smaller specimen, but only lightly interdigitated to it in 

 the larger. The more or less vertical anterior face of the 

 ethmoid supports the posteromedial ends of the premax- 

 illaries and maxillaries. The lateral surface of the anteri- 

 or one-third of the ethmoid is concave, so that when it 

 articulates laterally with the equally concave medial sur- 

 face of the palatine a spacious canal is left between the 

 two bones. Through this canal run the nerves and blood 

 vessels from the similar canal between the medial surface 

 of the prefrontal and lateral surface of the ethmoid car- 

 tilage. 



Vomer. — A narrow shaft throughout its length, 

 except anteriorly where it becomes somewhat expanded 

 dorsally to articulate by fibrous tissue with the postero- 

 medial arms of the premaxillary and maxillary; articu- 

 lates by interdigitation posteriorly with the concave 

 anterior end of the parasphenoid, laterally with the 

 palatines, and anterodorsally with the ethmoid. Postero- 

 dorsally the ethmoid cartilage intervenes between the 

 dorsal surface of the vomer and the ventral surface of the 

 ethmoid. 



Mandibular Region. 



Hyomandibular. — Very wide for most of its length, 

 only tapering to a stout shaft for a short distance antero- 

 ventrally; cartilage filled at its dorsal and anteroventral 

 edges; articulates by fibrous tissue dorsally with the 

 elongate concavity formed anterolaterally by the 

 sphenotic, anteromedially by the prootic, and pwsteri- 

 orly by the pterotic. The hyomandibular articulates by 

 fibrous tissue along its posterior edge with the preoper- 



Metapterygoid. — Large, thick, more or less square; 

 cartilage filled at its anterior edge; articulates by fibrous 

 tissue anterodorsally with the mesopterygoid, anteriorly 

 with the quadrate, and posteriorly with the hyomandib- 

 ular. Ventrally the metapterygoid slightly overlies and 

 interdigitates with the symplectic and also articulates by 

 fibrous tissue with the interhyal. 



Symplectic. — Large and elongate; cartilage filled at 

 its posterior edge; articulates dorsally by slight inter- 

 digitation with the overlying metapterygoid, while it ar- 

 ticulates by fibrous tissue posteroventrally with the 

 preoperculum and interhyal, and anteroventrally with 

 the overlying quadrate. 



Palato-Pterygoid Region. 



Palatine. — Expanded into a thick plate postero- 

 ventrally, but becoming laterally expanded anterodor- 

 sally; articulates by firm interdigitation along the ante- 

 rior half of its dorsomedial edge with the ethmoid and 

 along the anterior half of its ventromedial edge with the 

 vomer. The palatine is equally firmly interdigitated pos- 

 terodorsally with the prefrontal and posteroventrally 

 with the parasphenoid. The medial surface of the upper 

 region of the anterior half of the palatine is concave, so 

 that a canal is formed between it and the ethmoid, as de- 

 scribed previously. The medial and anterior surface of 

 the anterodorsal end of the palatine forms the articular 

 facet for support through fibrous tissue of the lateral sur- 

 face of the posteromedial wing of the maxillary. 



Ectopterygoid. — Expanded posteriorly; only 

 slightly curved along its anterior edge; articulates by fi- 

 brous tissue dorsally with the palatine and ventrally with 

 the quadrate, while posteriorly it articulates by fibrous 

 tissue and slight interdigitation with the mesopterygoid. 

 The palatine and quadrate slightly overlie the ec- 

 topterygoid, while the ectopterygoid slightly overlies the 

 mesopterygoid. 



Mesopterygoid. — Thin; irregular in its posterior 

 and ventral outline; articulates by slight interdigitation 

 anteroventrally with the ectopterygoid and by fibrous 

 tissue anteriorly with the palatine, ventrally with the 

 quadrate and posteroventrally with the metapterygoid. 



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