GREGORY: FISH SKULLS 



139 



The cranium (neurocranium) of a large tarpon (Fig. 32) shows the family characters 

 as well as many primitive isospondyl characters. The cranium as a whole is wedge-like 

 from front to rear, the enlarged dense vomer receiving the thrusts from the upper jaw as 

 well as from the skull-roof. The large orbit is supported anteriorly by the prominent 

 lateral ethmoid (parethmoid), above which is a thin prefrontal. The latter bears a branch 

 of the supraorbital lateral-line canal. 



The posterior end of the thin skull-roof is lifted high above the level of the brain tube 

 by the intrusion of the trapezius and the dorsal muscles of the flanks, which extend forward 



epiof 





Tarpon atlanllcus 



Fig. 31. Tarpon atlanticus. 

 N.B. The "scale bone" (= supratemporal of Owen and Starks and Ridewood = extrascapular in part of Allis) has been 

 removed, exposing the posttemporal and pterotic. 



through the large posttemporal fossae. The skull-roof is supported by vertical plates of 

 the supraoccipital and epiotics, which are prolongations of the otic part of the chondro- 

 cranium. In the tarpon the dorsal plate of the supraoccipital extends forward a short 

 distance beneath the posterior end of the parietals, but is widely separated from the frontals 

 in the top view (Fig. 33). In Elops, however, Ridewood (1904a, p. 37) notes that the 

 dorsal supraoccipital extends well forward beneath the posterior parts of the frontals. 



The brain trough beneath the skull-roof is stoutly built, the posterior part being 

 flanked by the greatly enlarged otic elements. The ali- and orbito-sphenoids are widened 



