the exoccipitals, but, rather, by the posterodorsal sur- 

 face of the basioccipital. From the posterior end of its 

 ventromedial edge the exoccipital possesses a modified 

 condyle in the form of a posteroventral process that ar- 

 ticulates by fibrous tissue with the lateral surface of the 

 neural arch and centrum of the first vertebra. 



Supraoccipital. — A rounded plate anteriorly, but 

 drawn out posteriorly into a long, laterally compressed 

 spine; cartilage filled along all of the edges of its rounded 

 anterior portion; articulates by interdigitation postero- 

 laterally with the epiotics and anteriorly and antero- 

 laterally with the frontals. Along the middle of its an- 

 terior end, as seen dorsally, the supraoccipital is broadly 

 overlain by the posteromedial edges of the frontals. The 

 supraoccipital spine is drawn out posteriorly between the 

 bifid neural spine of the first vertebra and sometimes 

 reaches posteriorly to above the second vertebra. The an- 

 terior half of the ventral edge of the supraoccipital spine 

 articulates by tough fibrous tissue with the dorsomedial 

 edges of the epiotics and exoccipitals. 



Otic Region. 



Pterotic. —Cartilage filled along its anteromedial 

 edge; articulates by interdigitation posteromedially with 

 the exoccipital, dorsomedially with the epiotic, antero- 

 dorsally and along the lateral part of its anteroventral 

 edge with the sphenotic, and anteroventrally with the 

 prootic. At the anterodorsal edge of its most laterally ex- 

 panded portion the pterotic articulates by fibrous tissue 

 with the posterolaterally projecting arm of the frontal. 

 Along the middle of its posterior surface the pterotic has 

 a concavity for articulation by fibrous tissue with the 

 supracleithrum. In the middle of its ventral surface the 

 pterotic articulates by fibrous tissue with the hyoman- 

 dibular. 



Sphenotic. — Broadly cartilage filled at its medial 

 edge; articulates by interdigitation anterodorsally and 

 dorsomedially with the frontal, posteromedially on its 

 dorsal surface with the epiotic, posterodorsally with the 

 pterotic, posteromedially on its ventral surface with the 

 pterosphenoid, and anteroventrally with the frontal. 

 Posteromedially on its ventral surface the sphenotic ar- 

 ticulates with the hyomandibular by fibrous tissue. 



Epiotic. —Flat, more or less rounded; broadly 

 cartilage filled along all of its edges of articulation with 

 the other cranial bones; articulates by interdigitation an- 

 teriorly with the frontals, anteromedially with the round- 

 ed anterior portion of the supraoccipital, anterolaterally 

 with the sphenotic, posterolaterally with the pterotic, 

 and posteromedially with the exoccipital. The medial 

 edges of the two epiotics articulate with one another and 

 with the ventral edge of the supraoccipital spine by fi- 

 brous tissue. 



teriorly; articulates by interdigitation anteroventrally 

 with the dorsolateral wing of the parasphenoid, antero- 

 dorsally mostly with the sphenotic but also with the 

 pterosphenoid, laterally with the sphenotic, postero- 

 laterally with the pterotic, and anteromedially with the 

 parasphenoid. From about the middle of its vertical 

 anteromedial edge the prootic possesses a thin splint of 

 bone projecting medially almost to the midline of the 

 skull, where it articulates by fibrous tissue with the 

 splintlike projection from the other prootic. These 

 delicate spines are evidently all that remains of the dor- 

 sal roofing of the myodome. The small myodome is now 

 roofed over only by a sheet of dense fibrous tissue which 

 begins anteriorly where it binds together the two medial 

 projections of the prootics and continues on posteroven- 

 trally to the floor of the cranial cavity, attaching pos- 

 teriorly to the region where the parasphenoid and basioc- 

 cipital interdigitate with the prootics. The myodome is 

 thus enclosed dorsally mainly by a fibrous tissue sheet, 

 and only at its upper anterior edge is the roof enclosed by 

 the medial projections of the prootics. Laterally the 

 myodome is bordered by the medial surfaces of the 

 prootics, ventrally by the dorsal surface of the para- 

 sphenoid, and posteriorly by the anterior end of the 

 basioccipital. 



Orbital Region. 



Frontal. — Laterally expanded in the middle of its 

 length; with a long posterolaterally directed arm. The 

 bone is generally dense and hard, but along the approxi- 

 mately anterior two-thirds of its medial portion a layer of 

 spongy connective tissue is present between the medial 

 surfaces of the two frontals. This spongy connective tis- 

 sue layer extends laterally into the frontal for about one- 

 fourth or one-fifth the width of the bone and anteriorly it 

 becomes cartilaginous and continuous with the ethmoid 

 cartilage. The frontal articulates by interdigitation dor- 

 somedially in the midline of the skull with its opposite 

 member, anteriorly with the ethmoid, which it broadly 

 overlies, anterolaterally with the prefrontal, postero- 

 laterally with the sphenotic, posteriorly on its dorsal sur- 

 face with the epiotic, and posteromedially on its dorsal 

 surface with the supraoccipital. From above the region 

 where it articulates with the sphenotic, the frontal 

 possesses a long posterolaterally directed process that ar- 

 ticulates by fibrous tissue with the anterodorsal edge of 

 the most laterally expanded portion of the pterotic. The 

 lateral fossa thus enclosed is bordered above by the fron- 

 tal and below by the sphenotic and pterotic. On its ven- 

 tral surface the frontal sends a ventromedially directed 

 process into the deeply concave dorsal surface of the ver- 

 tical interorbital projection of the parasphenoid, with ex- 

 tensive interdigitation occurring between the two bones. 

 Just lateral to its ventromedial projection, the frontal is 

 broadly overlain by the pterosphenoid, with slight inter- 

 digitation occurring between the two surfaces. 



Prootic. — Cartilage filled along all of its edges of 

 articulation with the other cranial bones, except an- 



Prefrontal. — In the form of a dorsolaterally ex- 

 panded column; cartilage filled at its rounded ventral 



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