Nos. IAND2.] ANATOMY OF SCOMBER SCOMBER. i^y 



interoperculum of Ainia, or of the enlarged dorsal branchiostegal 

 ray of that fish, seems an open question. Anterior to the point 

 where it is bound by fibrous tissue to the ceratohyal, the two bones 

 are connected by a wide and delicate membrane which forms part 

 of the floor of the movith cavity. The fibrous tissues that seem 

 to represent the ligamentum mandibulo-hyoideuni, lie in the 

 tissues along the internal surface of the bone, but, as already 

 stated, they are not the strongly developed ligament found in 

 Amia, the interoperculum itself, of Scomber, and the ligamentous 

 or fibrous tissues that bind and connect it with the ceratohyal and 

 mandible, seeming to, in part or in whole, replace the ligament. 



In Gegenbaur's figure of AlcpocepJiahis (No. 29, Fig. i) the 

 interoperculum seems to lie external to the ventral edge of the 

 preoperculum, differing in this from Scomber. There is nothing 

 in the bone in Scomber, more than in that of Alepocephalus, to 

 solve the question raised by Gegenbaur as to the arch to which the 

 bone primarily belongs, the hyoid or the mandibular. 



The Branchiostegal Rays (BRG) are usually seven or eight 

 in number. The four proximal ones are attached to the lateral 

 surface 'of the ceratohyal, near its inferior edge, varying some- 

 what in their position along that edge. Two are always attached 

 to the proximal ossification of the element, the third one being 

 sometimes attached to the same ossification, sometimes to the carti- 

 laginous interspace between that ossification and the distal one, 

 and sometimes to the latter ossification. The fourth ray was 

 always attached to the distal ossification, near the distal end of 

 the wider, blade-like portion of the piece. The three or four 

 distal rays are always attached to the mesial surface of the inferior 

 edge of the shank of the lower ossification. The bases of all the 

 rays are flattened and enlarged, and slight depressions on the 

 ceratohyal usually mark their places of attachment. In the recent 

 state the two most dorsal rays lie internal to the interoperculum, 

 the third ray lying along the ventral edge of that bone. 



The ramus hyoideus facialis lies, as in Amia, internal to all the 

 branchiostegal rays. 



The Truncus Arteriosus reaches the ventral surface of the 

 basal line immediately in front of the turned-down posterior end of 

 of the third basibranchial. There, having turned slightly upward 



