FISHERY BULLETIN: VOL. 82, NO. 4 



be seen a number of small foramina for the 

 branches of the supraorbital nerve trunk. The 

 laterosensory canals of the frontals are evident 

 on the pterotic crests as a series of pores. 



In Acanthocybium, the frontals are separated 

 from each other by the dorsomedian pineal fenes- 

 tra lying just in front of the supraoccipital at the 

 level of the pterosphenoids and another anterior 

 fontanel just posterior to the ethmoid bone (Fig. 

 13a). A smaller, more oval pineal opening is 

 present between the posterior ends of the frontals 

 in Grammatorcynus (Fig. 13b). When viewed 

 through the pineal fenestra, a part of the dorsal 

 surface of the parasphenoid is visible through the 

 opening of the brain chamber between the ptero- 

 sphenoids. There is a deep depression on the 

 frontals mesially, just anterior to the pineal fe- 

 nestra. This depression becomes shallower ante- 

 riorly, becoming confluent with the dorsal surface 

 of the frontals. In Scomberomorus , the frontals 

 join mesially along the median line on the neuro- 

 cranium where they form the anterior half of the 

 median ridge whose posterior half is composed of 

 the supraoccipital crest. In all but three species of 



Scomberomorus, the left and right frontals are 

 attached very closely to each other such that 

 there is no gap between them. However, in S. 

 commerson and S. cavalla, there is a long narrow 

 slit between the left and right frontals, but it is 

 not a fenestra in the true sense, as the lower parts 

 of the bones are very closely approximated. A 

 third condition is found in S. sinensis. Here the 

 anterior part of the median ridge is almost absent 

 and there is a wide gap between the left and right 

 frontals. The interorbital commissures of the lat- 

 eralis system are developed a little anterior to the 

 middle of each frontal in the form of two pores at 

 the margin of the median ridge which lead into 

 oblique tubes downwards and posteriorly. An- 

 other pair of commissures of the lateralis sys- 

 tem is developed along the anterolateral margin 

 of the frontals. These sensory canals are not 

 developed in Acanthocybium and Grammatorcy- 

 nus. 



Pterosphenoid. — The pterosphenoids (alisphe- 

 noids) form the posterodorsal region of the orbit. 

 They abut the basisphenoid and prootics posteri- 



FlGURE 20. — Left nasal bones in lateral view. a. Scomberomorus cavalla, Miami, 797 mm FL, 2x . b. Scomberomorus sinensis, 

 Tokyo, 1,850 mm FL, lx. c. Acanthocybium solandri, Revillagigedos Is., 1,068 mm FL, 1.5 x. d. Grammatorcynus bilineatus, 

 Queensland, 521 mm FL, 3 x . 



570 



