exterior at the base of the posterior bifurcation of the 

 parasphenoid, while anteriorly it opens into the 

 myodome where the anterior end of the basioccipital 

 forms the posterodorsal and posterolateral walls of the 

 myodome. 



Exocclpital. — Cartilage filled at its dorsal, lateral, 

 and ventral edges; articulates by interdigitation dorsally 

 with the epiotic, anteroventrally with the prootic, ventro- 

 medially with the basioccipital and laterally with the 

 pterotic, while dorsomedially it interdigitates with its op- 

 posite member above the foramen magnum. The 

 foramen is entirely surrounded by the exoccipitals, ex- 

 cept ventromedially where it is bounded by the upper 

 surface of the basioccipital. Posteromedially the exoc- 

 cipitals interdigitate with the neural spine of the first 

 vertebra. An exoccipital condyle is present only in the' 

 form of a slightly posteriorly elongate region of the 

 posteroventral end of the exoccipital, the short condyle 

 overlying the anterolateral surface of the lower neural 

 arch region of the vertebra just above the region of the 

 centrum. The neural processes from either side of the 

 first vertebra meet and interdigitate in the midline above 

 the neural canal, forming, in conjunction with the exoc- 

 cipitals to which they are also sutured, a completely 

 enclosed bony well in which the shaftlike end of the first 

 basal pterygiophore of the spiny dorsal fin is immovably 

 held by fibrous tissue. The bony bottom of this well is 

 formed mainly by the exoccipitals where they meet 

 medially to roof over the foramen magnum. 



Supraoccipital. — Dome-shaped; its stout rounded 

 anterodorsal edge forming the apex of the cranium and 

 its posterior surface concave; cartilage filled along most 

 of its ventral edges; articulates through interdigitation 

 posteroventrally with the epiotics and anteroventrally 

 with the frontals, the frontals overlying the anterolateral 

 edges of the supraoccipital. 



Otic Region. 



Pterotic. — Cartilage filled along most of its edges 

 of articulation with the other cranial bones; articulates 

 through extensive interdigitation posterodorsally with 

 the epiotic, posteromedially and ventromedially with the 

 exoccipital, anteromedially with the prootic, and antero- 

 laterally and anterodorsally with the sphenotic. The 

 anteroventral end of the pterotic is the main support for 

 the hyomandibular, its extreme anteroventral edge abut- 

 ting against the rear half of the dorsal end of the hyoman- 

 dibular while a sturdy ventral flange from its ventro- 

 lateral edge broadly overlies the posterodorsal region of 

 the lateral surface of the hyomandibular. While the ar- 

 ticulation between the pterotic and hyomandibular is 

 through fibrous tissue, it is very firm and relatively im- 

 movable, especially so because of the presence of the ven- 

 tral flange of the pterotic broadly overlying the hyoman- 

 dibular. Much of the posterolateral surface of the 

 pterotic is overlaid by the posttemporal, to which it is 

 firmly interdigitated. 



Sphenotic. — Cartilage filled along all of its edges of 

 articulation with the other cranial bones; articulates by 

 extensive interdigitation anteromedially with the 

 prootic, pterosphenoid, and frontal in the posterior wall 

 of the orbit, respectively from below to above. Laterally 

 on the skull the sphenotic articulates by interdigitation 

 dorsally with the frontal and epiotic and posteriorly with 

 the pterotic. Posterodorsally the sphenotic inter- 

 digitates for a short distance with the anterodorsal edge 

 of the posttemporal. Anterolaterally the sphenotic helps 

 form the concave groove that supports the dorsal edge of 

 the hyomandibular. The sphenotic forms the antero- 

 lateral part of the groove, the anteromedial part being 

 formed by the prootic and the posterior half by the 

 pterotic. The articulation of all these bones with the 

 hyomandibular is through fibrous tissue. 



Epiotic. — Cartilage filled along all of its edges of 

 articulation with the other cranial bones; articulates 

 through extensive interdigitation posterodorsally with 

 the supraoccipital and anterodorsally with the frontals. 

 Medially the edges of the two epiotics interdigitate with 

 one another, while posteroventrally they interdigitate 

 with the exoccipital and pterotic. Anteroventrally the 

 epiotic interdigitates with the posterodorsal region of the 

 sphenotic, while the extreme posterolateral edge of the 

 epiotic is broadly overlain by the upper end of the post- 

 temporal, with which it interdigitates. Ventromedially 

 on the posterior surface the epiotic helps form a very 

 short portion of the upper anterior region of the bony well 

 supporting the shaft of the first basal pterygiophore of 

 the spiny dorsal fin, while the main support for this shaft 

 is the portion of the well formed by the exoccipitals and 

 neural spine of the first vertebra. 



Prootic. —Cartilage filled along all of its edges of 

 articulation with the other cranial bones, except an- 

 teriorly; articulates by extensive interdigitation antero- 

 dorsally with the pterosphenoid, anterolaterally with the 

 sphenotic, posterolaterally with the pterotic, posteriorly 

 with the exoccipital, and posteromedially with the 

 basioccipital. The prootic interdigitates along all of its 

 length medially with the parasphenoid, while laterally 

 the prootic helps support the dorsal head of the hyoman- 

 dibular. The lateral walls of the myodome are formed by 

 the ventromedial surfaces of the prootics, while the dor- 

 sal walls of the myodome are formed by the medially 

 directed horizontal shelves, which are attached to one 

 another through extensive interdigitation, from the ven- 

 tromedial surfaces of the two prootics. The prootics also 

 form the upper two-thirds to three-fourths of the anterior 

 wall of the myodome. 



Orbital Region. 



Frontal. — Wider posteriorly than anteriorly where 

 it tapers to a blunt point above the posterior end of the 

 ethmoid and medial to the prefrontals; articulates by ex- 

 tensive interdigitation posteromedially with the supraoc- 

 cipital, whose anterior edge it broadly overlies, pos- 



