COLLETTE and CHAO: SYSTEMATICS AND MORPHOLOGY OF THE BONITOS (SARDINI) 



SPHENOTIC PTEROTIC 



PINEAL FORAMEN 

 FRONTAL 

 LATERAL ETHMOID 



VOMER 



INTERCALAR 



EXOCCIPITAL 



ETHMOID 



PARIETAL 



SUPRAOCCIPITAL 



EPIOTIC 



Figure 13.-Dorsal view of skull of Cybiosarda elegans. Western Australia, 422 mm FL. X's indicate the points of attachment of 



intermuscular bones. 



ETHMOID REGION.-This region is composed 

 of the ethmoid, lateral ethmoid, and vomer. The 

 nasal bone lies lateral to the ethmoid and lateral 

 ethmoid and, therefore, is included here. 



Ethmoid. -The ethmoid (dermethmoid) is the 

 most anterodorsally located bone of the 

 neurocranium. It has a smooth flat dorsal surface, 

 slightly convex at the median posterior end, to 

 receive the frontal bones. It connects ventrally to 

 the vomer and posteriorly to the lateral ethmoids 

 with rough and porous sutures. The anterior 

 border of the ethmoid is nearly straight in Or- 

 cynopsis (Figure 14), but is concave in the other 

 genera with an anteromedian projection and an 

 anterolateral horn on each side. 



Lateral Ethmoid.-The paired lateral ethmoids 

 (parethmoids) form the posterolateral wall of the 

 ethmoid region and the anterior wall of the orbit 

 with an olfactory foramen on each side. The lateral 



ethmoid articulates with the ethmoid anterodor- 

 sally, with the frontal bone posterodorsally, with 

 the parasphenoid posteroventrally, and with the 

 vomer anteroventrally. The posterolateral process 

 of the lateral ethmoid serves as an articulating 

 surface for the lachrymal, ectopterygoid, and the 

 entopterygoid. In ventral view, this articulating 

 surface area is small in Cybiosarda, slightly larger 

 in Allothunnus, and most expanded in the species 

 of Sarda, (Figures 15, 18, 19). In Orcynopsis and 

 Gymnosarda, it is an elongate narrow strip 

 (Figures 16, 17). The lateral expansions of the 

 lateral ethmoids in bonitos resemble those of more 

 primitive scombrids in being wider than in more 

 advanced genera. 



Vomer.-The vomer is the most anteroventrally 

 located bone of the cranium. It is located beneath 

 the ethmoid and the lateral ethmoids. Its pointed 

 posterior end fits into the V-shaped anterior 

 projection of the parasphenoid to form the sup- 



539 



