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DIL ATATOR F S S A. 



The dilatator fossa of Scorpaena is a small pit that lies directly above the interval between 

 the two articular facets for the hyomandibular, near the dorso-lateral edge of the skull. Its posterior 

 portion is enelosed in the pterotic, its anterior portion in the sphenotic. Between these two bones 

 there is, in the lateral edge of the roof of the fossa, an interval, which leads onto the roof of the 

 primordial cranium but is covered by the purely dermal postfrontal bone. The fossa gives origin to a 

 small superficial bündle of the dilatator operculi muscle, and corresponds to the deeper, posterior 

 portion, only, of the large dilatator groove of my descriptions of Scomber. If the dilatator muscle 

 were here, in Scorpaena, to push upward through the interval between the pterotic and sphenotic, 

 it would lift the postfrontal from the dorsal surface of the primordial cranium, and occupying the 

 region between the pterotic and postocular spinous ridges, give rise to the dilatator groove of Scomber. 



In the laottom of the fossa there are two openings. The anterior one opens directly into the 

 oticus canal and transmits a vein which is associated with the ramus oticus. The other transmits 

 a vein that comes from regions median to the oticus, between the primary skull and the overlying 

 dermal bones. 



The dilatator fossa and groove of the nomenclature here employed are the lateral temporal 

 fossa or groove of Eidewood's recent descriptions of the teleostean skull. But Ridewood does not call 

 attention to the marked difference between these fossae and grooves, as just above set forth, and 

 doubtless did not recognize it. In both Elops and Megalops, for example, the lateral temporal groove 

 of Ridewood's descriptions would seem to be the homologue of the dilatator groove of Scomber; 

 while in both Albula and Bathythrissa, the lateral temporal fossa would seem to be the homologue 

 of the dilatator fossa of Scorpaena; the lateral temporal grooves and lateral temporal fossae of his 

 descriptions then not being equivalent. 



In the Clupeidae, there would seem to be, from Ridewood's descriptions, a dilatator groove 

 similar to the groove in Scomber. 



M E S E T H JI I D. 



The mesethmoid has a keel-shaped anterior portion, the keel directed dorsally, and a thin 

 tapering posterior portion which is concave longitudinally, on its dorsal surface, and ends posteriorly 

 in a point. Between these two portions, and at about the middle of the length of the bone, two stout 

 prong-like processes arise, one on either side, and project upward and slightly laterally and forward. 

 The hind edge of each process is usually slightly convex, curving upward, forward and laterally, 

 while the ventral half of the anterior edge is slightly concave ; the whole process having the appear- 

 ance of a hörn projecting upward, forward and laterally but with the point cut off obliquely, so that 

 a flat surface is presented almost directly forward. This flat surface gives origin to the ethmo-maxil 

 lary ligament, while the lateral surface of the process gives support and attachment to the hind eno 

 of the nasal bone. This stout and prominent process has long been known and is the homologue of 

 the quite differently appearing dorso-lateral process of my descriptions of Scomber, a fact I did not 

 recognize when describing that fish. It has been called the mesethmoid process in certain descriptions 

 of the Scorpaenidae, a name which I adopt as much preferable to the term employed by me. 



The median keel on the dorsal surface of the anterior portion of the mesethmoid forms the thick 

 but low internasal wall of the skull. It extends backward a varying distance between the two meseth- 

 moid processes. and on it the cartilaginous rostral slides backward and forward, the tapering hind end 



