Fipire \9S.—Lagocephalus laevigatua: 



posterior view of skull (left); above, 



lateral and posterior views of first 



abdominal vertebra; posterior view of 



orbit (right) (cross section of skull; 

 dashed lines represent cut surfaces of 

 frontals, pterosphenoids, and parasphenoid); 

 composite based on several 



61.4-166 mm SL, Gulf of Mexic 



Prootic. — Cartilage filled along all of its edges of 

 articulation with the other cranial bones, except 

 anteriorly; articulates by interdigitation anteroventrally 

 with the dorsolateral wing of the parasphenoid, antero- 

 dorsally with the pterosphenoid and sphenotic, ventro- 

 laterally with the sphenotic, ventromedially with the 

 parasphenoid, and posteromedially on its ventral sur- 

 face with the basioccipital. The more or less vertical an- 

 teromedial edge of the prootic possesses a slight medial 

 protuberance which probably marks the former dorsal 

 limit of the now absent bony myodome and corresponds 

 to the medially directed prongs representing the rudi- 

 ments of the bony dorsal roof of the myodome in such 

 tetraodontids as Lagocephalus laevigatas. The func- 

 tional myodome is roofed over by a fibrous tissue sheet 

 between the two prootics and the region of articulation 

 between the parasphenoid and basioccipital. The func- 

 tional myodome is thus bounded dorsally by a fibrous 

 tissue sheet, laterally by the prootics, ventrally by the 

 dorsal surface of the parasphenoid, and posteriorly by 

 the anterior end of the basioccipital. 



Orbital Region. 



Frontal. — Thin throughout most of its length, ex- 

 cept posterolaterally; articulates by slight interdigi- 

 tation dorsomedially with its opposite member, while its 

 ventromedial edge makes fibrous tissue contact with the 

 cartilaginous rod which is continuous anteriorly with the 

 ethmoid cartilage; articulates by slight interdigitation 

 anteriorly with the ethmoid, which it slightly overlies, 

 anterolaterally with the prefrontals, which it broadly 

 overlies, posteromedially with the supraoccipital, which 

 it slightly overlies, posteriorly with the epiotic, and pos- 

 terolaterally with the sphenotic. In the posterior wall of 

 the orbit the frontal articulates laterally with the spheno- 



tic and medially with the pterosphenoid. The most dis- 

 tinctive feature of the frontal concerns the shape of its 

 laterally expanded posterior portion. Just behind the 

 region that forms the posterolateral wall of the orbit, the 

 dorsal surface of the frontal possesses a thin laterally di- 

 rected flange. This flange makes contact with the ex- 

 treme posterolateral edge of the frontal, just above the 

 area of articulation between the frontal and sphenotic. In 

 small specimens the articulation between the flange of 

 the frontal and the posterolateral edge of the portion of 

 the orbital wall formed by the frontal is by close apposi- 

 tion through fibrous tissue, but in larger specimens these 

 two surfaces of the frontal tend to fuse together. The 

 space between the lateral flange and the posterolateral 

 region of the orbital wall is filled with a muscle mass 

 which connects ventrally with the uppermost end of the 

 operculum (see Winterbottom 1974). 



Prefrontal. — Thin and more or less flattened 

 dorsally, but tapering to a stout column anteroventrally; 

 cartilage filled at its ventromedial edge, where it is con- 

 tinuous with the ethmoid cartilage; articulates by slight 

 interdigitation posterodorsally with the frontal, antero- 

 dorsally with the ethmoid, and anteroventrally with the 

 parasphenoid. 



Parasphenoid. — Elongate, with a well-developed 

 ventral keel in the suborbital region. The anterior end of 

 the parasphenoid is concave and receives the posterior 

 end of the vomer, with which it interdigitates. The dorsal 

 edge of the parasphenoid anterior to the orbit is slightly 

 concave and interdigitates with the posterior half of the 

 ventral edge of the ethmoid, while just posterior to this 

 region it interdigitates with the base of the prefrontal. 

 The flattened, somewhat laterally expanded, posterior 

 end of the parasphenoid slightly overlies and interdigi- 



