COMPARATIVE STUDY OF SCOMBROID FISHES. 
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they are thin banes, folded in different directions. Tire prefrontals are loosely 
joined with each other, as well as with other bones, except the vomer. They 
are longer than broad, and have only one articulating surface for the palatine 
in the Scombridæ, and also in the Cybiidæ, except Sarda and Gymnosarda. 
In these genera and also in the Plecostei the bones are nearly as long as 
broad, and have no articulating surfaces for the palatiue. The olfactory nerve 
passes through the middle of the prefrontal. 
The vomer is an anterior median bone, thickened at the anterior end, but 
gradually attenuated behind. The bone lies below the parasphenoid, and is 
joined to it at the posterior part, at the anterior part it is joined to the 
ethmoid and prefrontals with suture. The ventral surface of the thick anterior 
end of the vomer is often concave, otherwise nearly flat and is armed with 
villous teeth. These teeth are grouped generally in a median longitudinal 
band ; but in Scomber they are grouped in paired separate patches. 
The frontals are large, paired bones, uniting with each other at the 
median line, and forming a bridge over the orbit, they connect the brain- 
case with the ethmoidal bones. Their anterior paid is tliin, flat, and narrow, 
while the posterior part is broad, and more or less bent downward. From 
the centre of the dorsal surface of each bone, five striæ radiate in all 
directions. This central portion is thick. Anteriorly the frontals rest on the 
entire dorsal surface of the prefrontals and the posterior part of the ethmoid. 
Posteriorly they articulate with the supraoccipital, parietals, sphenotics, pterotics, 
and alisphenoids. In the scombroid fishes the frontals do not unite nor meet 
closely with each other at the posterior end, just above the alisphenoid. In 
the Scombridæ we find only a slit there, in some fishes of the Cybiidæ the 
slit is pretty large (figs. 38-40), and in the Plecostei it is large and always 
conspicuous. Before the slit or foramen the frontals unite with each other at 
the median line. In the Scombridæ the frontals before the slit are thin, 
in the Cybiidæ they are thick, and in the Plecostei hollow. In the 
Thunnidæ near the anterior half of the slit there is a pit with rough walls 
for the attachment of a ligament connecting the skin to the skull. In the 
Cybiidæ and Plecostei the lateral external side of the frontal is raised and 
very thick, while the internal side is raised to form a median crest, continuous 
to the supraoccipital crest. Thus there is a broad furrow on the dorsal 
