the parasphenoid; articulates through cartilage and in- 

 terdigitation ventrolaterally with the pterotic, postero- 

 ventrally with the basioccipital and exoccipital, dorso- 

 medially with the pterosphenoid, and dorsolaterally with 

 the sphenotic. Along a short distance of the anterior edge 

 of its laterally expanded posterior portion the prootic ar- 

 ticulates through cartilage with the posterodorsal end of 

 the hyomandibular. The anteromedial region of the 

 prootic possesses a long forward extension under the or- 

 bit which makes contact by interdigitation with the 

 parasphenoid at the level of the prefrontals. A recurved 

 portion of this prootic subocular shelf is directed postero- 

 laterally and makes contact with the anterolateral region 

 of the rear half of the prootic, the two parts of the bone 

 interdigitating in this region just medial to the ar- 

 ticulation of the prootic with the dorsal edge of the 

 hyomandibular. Just ventral to this region of contact 

 between the posterolateral wing of the prootic shelf with 

 the rest of the prootic, the wing is thickened and ar- 

 ticulates by fibrous tissue with the dorsal surface of the 

 lateral region of the ossified Baudelot's ligament. The 

 medial edges of the prootics form the lateral walls of the 

 myodome, while medially directed shelves from the 

 medial edges of the prootics more or less meet in the mid- 

 line and articulate through cartilage with one another to 

 form the dorsal roof of the myodome. The anterior edge 

 of the myodome is formed by the prootic, except ven- 

 trally where it is formed by the parasphenoid. 



Orbital Region. 



Frontal. — Wide in the posterior half of its length, 

 then rapidly tapering to a point anteriorly; extending 

 throughout almost the entire length of the skull and a 

 relatively sturdy bone throughout its length; articulates 

 through cartilage and interdigitation posteromedially 

 with the supraoccipital and posterolaterally with the 

 epiotic and sphenotic, broadly overlying the latter. In the 

 posterior wall of the orbit the frontal articulates through 

 cartilage and interdigitation with the pterosphenoid and 

 sphenotic. The anterior prolongation of the frontal 

 broadly overlies and is held by fibrous tissue to the dorso- 

 lateral surface of the ethmoid. Immediately posterior to 

 where it begins to overlie the ethmoid, the ventral sur- 

 face of the frontal is held by fibrous tissue to the dorsal 

 surface of the prefrontal. 



Prefrontal. — Large and wedge-shaped; cartilage 

 filled along its medial edge where it is continuous with 

 the ethmoid cartilage; articulates by fibrous tissue dor- 

 sally with the broadly overlying frontal and ventrally 

 with the dorsal edge of the parasphenoid, the latter ar- 

 ticulation perhaps strengthened by slight inter- 

 digitation. Its major surface of articulation, however, 

 remains with the ethmoid cartilage, that broadly inter- 

 venes between the prefrontal and the ethmoid. 



Parasphenoid. —An elongate, mostly laterally com- 

 pressed, slab of bone; expanded in the middle of its 



length for articulation by interdigitation with the antero- 

 medial edges of the prootic shelves, and, more pos- 

 teriorly along its ventral edge, where it interdigitates 

 with the prootics and basioccipital. Dorsally in the region 

 of the orbit the parasphenoid has a large dorsal flange 

 which meets and interdigitates with the ventral flanges 

 of the pterosphenoids. Just anterior to this dorsal flange 

 the parasphenoid articulates by fibrous tissue and per- 

 haps slight interdigitation with the ventral end of the 

 prefrontal. Anterodorsally the parasphenoid articulates 

 by fibrous tissue and interdigitation with the ventral 

 edge of the ethmoid, while the extreme anteroventral 

 edge of the parasphenoid becomes concave for reception 

 of the posterior end of the vomer, with which it inter- 

 digitates. At its extreme posterior end the parasphenoid 

 bifurcates in the region that overlies the ventral surface 

 of the anterior half of the basioccipital. However, there is 

 no apparent opening into the myodome in this region 

 such as is found in triacanthoids and balistoids. Along its 

 laterally expanded ventral surface in the region of the 

 rear of the orbit the parasphenoid articulates by fibrous 

 tissue and perhaps slight interdigitation with the medial 

 ends of the ossified Baudelot's ligaments from either 

 side. 



Pterosphenoid. — Cartilage filled along all of its 

 edges of articulation with the other cranial bones, ex- 

 cept for a very short distance anteroventrally; ar- 

 ticulates through cartilage and interdigitation postero- 

 dorsally with the frontal, which somewhat overlies it, 

 posteriorly with the sphenotic, and posteroventrally with 

 the prootic. The anterior end of the pterosphenoid is 

 prolonged anteroventrally into a process which inter- 

 digitates with the dorsal edge of the dorsal flange of the 

 parasphenoid in about the middle of the orbit. 



Ethmoid Region. 



Ethmoid. —Elongate; laterally expanded and 

 somewhat rounded dorsally, but ventrally becoming 

 laterally compressed where it articulates by inter- 

 digitation and fibrous tissue with the parasphenoid, 

 which in the posterior region of the articulation overlies 

 the ventrolateral edges of the ethmoid; cartilage filled at 

 its posterior edge, where it is continuous with the eth- 

 moid cartilage; articulates by fibrous tissue dorsally with 

 the anterior prolongation of the frontal, which broadly 

 overlies the dorsolateral surface of the ethmoid. Antero- 

 ventrally the ethmoid articulates through cartilage and 

 slight interdigitation with the dorsal surface of the 

 vomer. At its anterior edge the ethmoid helps support, 

 through fibrous tissue, the upper jaw. 



Vomer. — A short, squarish block of bone with two 

 lateral expansions and a posterior tapering shaft; ar- 

 ticulates through cartilage and interdigitation dorsally 

 with the ethmoid and by interdigitation posteriorly 

 where its shaft fits into the concave anteroventral edge of 

 the parasphenoid. The anterior end of the vomer sup- 



