of the Fishery Board for Scotland. 



283 



the lower posterior part of this quadrilateral head there projects backwards 

 the facet for articulation with the operculum, and the enlarged part of the 

 hyomandibular gives mainly attachment to the muscle raising that bone. 

 From the upper part there passes downwards and slightly forwards a 

 narrow thick bar, the anterior edge of which projects somewhat outwards 

 as a thinner lamina, against which, and overlapping the main stem, -lies 

 the preoperculum. This outer ridge of the hyomandibular partly overhangs 

 a thin widened triangular portion (PI. XV. fig. 1, a.h.mri.) curved on its upper 

 surface, and which projects forwards from the inner anterior face of the 

 main stem. The apex of the triangle projecting forwards is terminated by 

 the small hook-shaped process already referred to as overlapped by the 

 similar process of the metapterygoid. 



To the strong blunt ventral end of the hyomandibular, and continuous 

 with it in nearly a straight line, is attached the symplectic (sym.), a narrow 

 rod-like bone, with its slightly expanded posterior end articulating with the 

 hyomandibular, while the narrowed rod lies partly against the ventral edge 

 and partly (its anterior end) in a groove on the inner ventral surface of the 

 quadrate. Articulating with the lower anterior corner of the quadrate is the 

 articular portion of the lower jaw (art.), the basal thickened ridge of which is 

 formed partly round Meckel's cartilage, which runs nearly to the symphysis 

 along the inner side of the strong thick lower border of the dentary (den.). 

 The anterior incurved part of the dentary bears small teeth, and is short, 

 almost the whole bone being expanded into an upstanding square-shaped 

 portion overlapped by the maxilla, its posterior edge slightly overlapping 

 the front of the triangular-shaped articular, while its ventral edge extends 

 backwards as a strong spine overlapping the lower articular edge almost to 

 the condyle. Just below the latter, and not forming part thereof, is a 

 very small solid angular (an.). 



The maxilla (mx.) extends backwards as far as the middle of the orbit in 

 the closed condition, but when widely open takes an almost vertical posi- 

 tion (PI. XV. fig. 1, mx.; PI. XVII. fig. 15, mx.). Its upper inner end is 

 flattened nodule, the inner edge of which meets its fellow of the opposite 

 side in the middle line. 



It consists of an elongated flattened external portion bearing minute 

 teeth along its ventral edge; rounded at its posterior lower end it is con- 

 tracted at its upper to pass into a short rod-like neck, which passes inwards 

 nearly at right angles to the expanded flat portion of the bone. On its 

 inner or posterior edge and middle of its length this neck bears a small 

 condyle, while it terminates in a flattened nodular triangular head. The 

 internal edge of this head meets its fellow of the opposite side, while the 

 condyle on its posterior corner articulates with the ethmoidal cartila- 

 ginous boss. The condyle behind the external end of the 'neck' articulates 

 with the outer end of the palatine, a cartilaginous pad intervening between 

 their surfaces ; consequently in the hollow formed between the two condyles 

 on the posterior edge of this dorsal and mesial neck of each maxilla lies part 

 of the ethmoid and palatine and the articular junction between them. 



Anterior to the maxillse are the short narrow premaxilke (pr.mx.). 

 Meeting with each other in a symphysis in the middle line, they pass 

 downwards in front of the backward hollow formed by the necks of the 

 maxillae, so as to leave a narrow skin-covered space (PI. XV. fig. 1,/.) between 

 them, and they terminate in a pointed end loosely attached by connective 

 tissue and skin to the upper anterior corner of the flattened part of the 

 maxilla. Just inside the median part of their anterior thin edge they each 

 bear about half a dozen sharp teeth. Their anterior edges form an almost 

 straight continuous line, there being no emargination at their symphysis. 

 Overlapping the posterior (lower) end of the maxilla is the jugal, its anterior 



