Sphenotic. — Cartilage filled along all of its edges of 

 articulation with the other cranial bones; articulates by 

 interdigitation anterodorsally with the frontal and 

 pterosphenoid, posterodorsally with the epiotic, postero- 

 ventrally with the pterotic and posttemporal, and antero- 

 ventrally with the prootic. 



Epiotic. — Cartilage filled along all of its edges of 

 articulation with the other cranial bones; articulates by 

 interdigitation dorsally with the supraoccipital, dorso- 

 laterally with the frontal, laterally with the sphenotic, 

 ventrolaterally with the pterotic and a short section of 

 the posttemporal, posteroventrally with the exoccipital, 

 and medially with its opposite member. The posterodor- 

 sal edge of the epiotic is deeply concave where it inter- 

 digitates with the supraoccipital, forming, with the latter 

 bone, the concavity in the skull in which is held by 

 fibrous tissue the anteroventral shaft of the first basal 

 pterygiophore of the spiny dorsal fin. 



Prootic. — Cartilage filled along all of its edges of 

 articulation with the other cranial bones, except antero- 

 medially; articulates by interdigitation medially with 

 the lateral surface of the parasphenoid, anteromedially 

 with the ascending fork of the parasphenoid, anterodor- 

 sally with the pterosphenoid, anterolaterally with the 

 sphenotic, and posteriorly with the pterotic. A concavity 

 is present in the middle of the ventral surface of the 

 prootic in which is held by fibrous tissue the anterior 

 half of the dorsal head of the hyomandibular. The medial 

 edges of the prootics form the lateral walls of the 

 myodome, while medially directed shelves from the 

 medial edges of the prootics interdigitate with one 

 another in the midline to form the dorsal roof of the 

 myodome. The anterior edge of the myodome is formed 

 by the prootics, except ventrally where it is formed by 

 the parasphenoid. The anterior end of the prootic is 

 prolonged anteriorly as a subocular shelf which serves for 

 muscle attachment. 



Orbital Region. 



Frontal. —Widest posteriorly, tapering to a point 

 anteriorly; its lateral edge above the orbit slightly uprais- 

 ed and thickened; articulates by interdigitation postero- 

 medially with the supraoccipital, which it slightly 

 overlies, posterolaterally with the sphenotic and pos- 

 teriorly with the epiotic. Posteriorly in the rear of the or- 

 bit it interdigitates with the pterosphenoid. The frontal 

 interdigitates anteriorly with the ethmoid and antero- 

 laterally with the prefrontal. On its ventral surface, the 

 medial edges of the frontals are narrowly separated by 

 the cartilaginous mass which is continuous anteriorly 

 with the remains of the ethmoid cartilage. 



Prefrontal. — Large and elongate; cartilage filled 

 along its medial edge; articulates by interdigitation dor- 

 somedially with the frontal, ventrally with the para- 

 sphenoid, and anteriorly with the ethmoid. Along most 



of its medial edge, the prefrontal is continuous with the 

 remains of the ethmoid cartilage. 



Parasphenoid. — Elongate, running almost the 

 entire length of the skull; ventrally expanded into a thin 

 keel along the anterior half of its length. The bifurcate 

 posterior end of the parasphenoid broadly overlies and 

 interdigitates with the basioccipital, roofing over the 

 longitudinal concavity in the ventral surface of the 

 basioccipital. Under the posterior region of the orbit, the 

 parasphenoid possesses a pair of short, slightly forked, 

 dorsolateral projections which interdigitate with the 

 prootics and form the anterior edge of the ventral region 

 of the myodome. Posterior to these dorsal wings, the 

 parasphenoid interdigitates with the ventromedial edges 

 of the prootics and, more posteriorly, with the ventral 

 surface of the basioccipital. Just anterior to the orbit, the 

 parasphenoid interdigitates with the base of the prefron- 

 tals. Anterior to the level of its articulation with the 

 prefrontals, the dorsal edge of the parasphenoid becomes 

 concave and fits around the ventral edge of the ethmoid 

 keel. At its anterior end the parasphenoid possesses a 

 short, narrow concavity into which fits and interdigitates 

 the posterior shaftlike portion of the vomer. 



Pterosphenoid. — Cartilage filled along all of its 

 edges of articulation with the other cranial bones; ar- 

 ticulates by slight interdigitation dorsally with the fron- 

 tal, laterally with the sphenotic, and ventrally with the 

 prootic. Medially the pterosphenoid articulates broadly 

 through cartilage and interdigitation with its opposite 

 member. 



Ethmoid Region. 



Ethmoid. — Wide and elongate; slightly expanded 

 laterally and ventrally at its anterior end; produced ven- 

 trally into a keel which is relatively low along most of its 

 length, but which increases in depth at its anterior end 

 above the shaftlike portion of the vomer; cartilage filled 

 at its posteroventral edge where it is continuous with the 

 remains of the ethmoid cartilage. The ventral edge of the 

 ventral flange of the ethmoid articulates by fibrous tissue 

 with the concave dorsal edge of the platelike portion of 

 the parasphenoid. At its posterior end the ethmoid ar- 

 ticulates by interdigitation laterally with the prefrontal 

 and dorsally with the frontal. The ethmoid articulates by 

 fibrous tissue anteroventrally with the anterior edge of 

 the vomer, while directly anteriorly the ethmoid supports 

 the posterodorsal edge of the upper jaw. 



Vomer. — Short; laterally expanded anteriorly but 

 tapering to a shaft posteriorly; articulates posteriorly by 

 slight interdigitation of its posterior shaftlike portion 

 with the concavity at the anterior end of the para- 

 sphenoid; articulates by fibrous tissue dorsally with the 

 anteroventral surface of the ethmoid and anterolaterally 

 with the medial surfaces of the palatines and the postero- 

 dorsal edges of the upper jaw. 



