7. SCIyliNA. 285 



cesses of the intermaxillary, and a posterior for the articulation with 

 the vomer ; the middle portion, flat and narrow, widening where it 

 passes into the extremitj^ of the bone ; this latter portion is extremely 

 broad> three times broader than the middle one ; at its inside it has 

 a ridge along each of the margins. The entii'e bone has a very solid 

 structure, and there are no vestiges of its having been separated into 

 two bones. The intermcuviUary is strong, but narrow ; its posterior 

 processes extend backwards to the level of the anterior margin of 

 the eye, being only one-half the length of the bone ; there is a 

 flat triangular process posteriorly. The mandihulary has a high, 

 sharp ridge at its outer side, running from the joint to the sym- 

 physis, and forming with the lower margin of the bone a deep chan- 

 nel : there are vestiges of four feeble ridges crossing the channel, 

 and extending from the longitudinal ridge to the lower margin. 

 These ridges are much more developed in other fishes vrith mucous 

 cavities on the skull, and di\ade the mandibulary channel into as 

 many ca\ities. 



The single parts of the tympanic bones may be well distinguished 

 from one another: the hypotympanic is joined to the praetympanic 

 by a narrow strip of cartilaginous tissue ; all the other parts form 

 together true sutures. The mesotympanic Is the narrowest, and 

 distinguished by a wide foramen. There is a cavity, closed by a mem- 

 brane only, between the pra;- and epitympanic ; the former is exceed- 

 ingly thin at its upper marginal j)art. The pterygoid is thin, nar- 

 row, extending nearly to the mandibulary joint ; the entopterygcdd is 

 composed of a moderately strong ossified strip along its suture with 

 the palatine and pterygoid bones, all the rest being exceedingly thin, 

 like the corresponding part of the praetympanic. The palatine bone 

 is more solid, quadrangular, with two of its sides free. 



The anterior part of the vomer is thick, and furnished with two 

 joints on each side, one for the palatine and the other for the max- 

 illary : there is a projecting flat process in front, separating the 

 maxillaries from each other. The palatal surface of the vomer is 

 slightly concave, and broadest between the joints for the palatines. 

 The posterior part of the vomer is finely tapering. The upper sur- 

 face of the skull is entirely occupied by that superstructure of bony 

 ridges and crests, by which the mucous cavities of the Scisenoids are 

 supported and formed. The occipital crest is raised from above the 

 foramen occipitale magnum, and separated into a posterior and su- 

 perior portion by a narrow transversal ridge-, which arises from the 

 occiput on the same level with the upper surface of the skull ; the 

 posterior portion is nearly twice as wide as the superior. There is, 

 on each side of the base of this portion, a horizontal, elongated, eDip- 

 tical foramen in the supraoccipital, absent in many Acanthopterygii^ 

 and vertical in others. The superior portion extends a little on 

 the frontal bones, and bifurcating emits two bars to form the middle 

 and largest cavity. This cavity occupies the middle of the upper 

 surface of the skull, and is elongate, quadrangular, with two pairs of 

 sides, with a posterior and anterior acute angle, and wjth a pair of 

 obtuse ones on the sides. The posterior pair of sides is much longer 



