THE CLUPEOID CIL\NIUM AND THE SWIMBLADDER 461 



5. The sphenotic hone 



This pyramid-shaped bone forms the extreme lateral part of 

 the anterior portion of the cranium (figs. 1, 2, and 9, SPH). 

 The ventral part of the bone articulates posteriorly with the 

 pterotic. Its upper part does not meet the pterotic posteriorly 

 and the interval between them is bridged by the lateral wing of 

 the frontal (fig. 3). Medially, the sphenotic bone articulates 

 with the prootic and alisphenoid; laterally and dorsally, it is 

 overlapped by the lateral wing of the frontal bone. The bone 

 is deeply excavated posteriorly, so that a cavity occupies a large 

 portion of its body. This cavity shares in th€ formation of the 

 lateral recess. 



6. The basisphenoid bone 



This bone is a thin, slightly curved, median plate of bone, 

 articulated between the front parts of the two prootics (fig. 7, 

 BSP). It forms most of the floor of the hypophysial fossa and 

 its posterior edge is the anterior margin of the hypophysial 

 foramen. A deep notch in the posteriolateral margin of each 

 side is converted into a foramen by articulation with the prootic 

 and gives passage to the oculomotor nerve. The anterior edge 

 of the bone forms the posterior margin of the optic foramen. 



7. The opisthotic bone 



This bone is almost rudimentary in the Clupeoids. It is a 

 somewhat rectangular scale-like bone overlying the articulation 

 between the exoccipital and pterotic bones (figs. 5 and 11, OPT). 

 It has no relation to the membranous labyrinth or swimbladder 

 diverticulum. 



8. The lateral wing of the frontal bone 



This is a thin scale of a bone extending down over the lateral 

 face of the skull (fig. 1, LWF). Near its origin from the main 

 part of the frontal, the posterior edge of the lateral wing forms 

 the anterior margin of the temporal foramen; the anterior edge 



