818 REPORT OF COMMISSIONEE OF FISH AND FISHERIES. [72] 



and anterior angle as to form a proper enlargement to support the 

 articular facet for the 'lyomandibular. Viewed from without, its lower 

 border overlaps for a couple of millimeters the suboperculum. This 

 latter bone is shaped as shown in Figs. 27 and 32. Anteriorly it de- 

 velops a pointed and upturned process, that lies between the lower 

 angle of the operculum and the upper angle of the interoperculum. 



The inter operculum has a quadrilateral outline, with the angles rounded 

 off. Externally it is well overlapped by the preoperculum, and is at- 

 tached to the mandible by ligament, while internally the epihyal and 

 interhyal of the hyoid arch rest against it. In texture these three 

 bones of the group are semi transparent and exquisitely marked with 

 radiating and wavy concentric lines. 



The preoperculum overlies all the other opercular bones, while it itself 

 is overlaid by the hyomandibular above and the quadrate below. It is 

 roughly crescentric in form, being carried to a gradually tapering point 

 above, and strengthened throughout its entire length by a raised ridge 

 of bone. On its inner aspect the lower limit of the hyomandibular, the 

 interhyal, and the symplectic rest against it (Fig. 32). 



It has been said that the opercular bones are but modified, or rather 

 transformed, branchiostegal rays. 



Situated beyond the opercula we discover another arcade of bones ; 

 this consists, from above downwards, of the hyomandibular, symplectic, 

 and quadrate, the chain constituting the suspensorium. They con- 

 nect, in Micropterus as in the osseous fishes generally, the cranium 

 with the lower jaw (Figs. 27 and 32, jET. M., Sym. and Qu.). By the 

 intervention of the interhyal, the hyomandibular has also suspended 

 fipom its lower extremity the hyoid arch, and its upper and poste- 

 rior angle, as we saw above, also articulates with the operculum. 

 The hyomandibular is compressed from side to side, expanded above, 

 to be gradually drawn down to a blunt point below, where it is united 

 through a common cartilaginous bridge with the apices of the interhyal 

 and symplectic. This latter element is wedged in between the quad- 

 rate and preoperculum, with the metapterygoid resting against its an- 

 terior border, it being merely a small bone that has been segmented off 

 from the hyomandibular. 



The quadrate is here, as is usually the case among fishes, a triangular 

 bone of some size, articulating with the mandible at its lower angle 

 (Fig. 27, Qu.). Against the upper half of its anterior border, by a very 

 close suture, the ectopterygoid is placed, forming a part of the con- 

 nection of the next arch beyond with the suspensorium. Upon the cra- 

 nium the hyomandibular articulates with the postfrontal and squamo- 

 sal in a long, narrow, longitudinal facet. 



The arch next beyond the suspensorium is the pterygopalatine arch. 

 It is made up of the metapterygoid, the ento- and ectoptergoid and the 

 palatine. This last element I have figured and suflSciently described 

 above. In a great many fishes the palatine is movably connected at 



