COMP.VRATIVE STUDY OF SCOMBROID FKHES. 313 



tliey arc thiu bones, foklod in ilill'oront dirwtions. The prefrontjils jms loosely 

 joined with each other, as well as with other Iwne?, except the vomer. They 

 are longer tlian broaJ, and have only one articulating surface for the palatine 

 in the Scombrida^ and also in the OybiidiO, except Sarda and Gymnoaarda. 

 In these genera and also in the Plecostoi the bones are nearly as long as 

 broad, and have no articulating surfiicos for the palatine. The olfactory nerve 

 Xrusses through the middle of the prefrontal. 



The vomer is an anterior median Ixine, thickentxl at the anterior end, but 

 gi-adually attenuated liehind. The bane lies below the p irasphenoid, and is 

 joined to it at the iiostoriov part, at the anterior part it is joined to the 

 ethmoid and prefi'ontals with suture. The ventral surface (jf the thick anterior 

 end of the vomer is often concave, otherwise nearlj' flat and is armed with 

 villous teotii. These teeth are grouped generally in a median longitudinal 

 bind ; but in Scomber they .are gi-oujied in paired s<^parate patches. 



The fi'ontals are largo, paired bones, uniting with each other at the 

 median line, and forming a bridge over tlie orbit, they connect the brain- 

 case with the ethmoidal bones. Their anterior part is thin, flat, and narrow, 

 while the \x)sterior part is broad, and more or less bant downward. From 

 the centre of the doi'sal surface of each bone, five striae radiate in all 

 directions. This centi'al portion is thick. Anteriorly the frontals rest on the 

 entire doreal sui-face of the in'efrontals 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 etxah other at the posterior end, just alx)ve the alisj)henoid. In 

 the Scombxidcie we find only a slit there, in some fishes of the Cybiidae 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 Hne. In the Scombridas the frontalis before the slit are thin, 

 in the Cybiidae they are thick, and in the Plecostei hollow. In the 

 Thurmida? nesu" the anterior half of the sUt there is a pit with rough walls 

 for the attachment of a ligament connecting the skin to the skull. In the 

 Cybiida) and Plecastoi 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 fun-ow on the dorsal 



