GREGORY: FISH SKULLS 



285 



occupy the long narrow area beneath and in front of the eye and are divided into several 

 superficial and deep heads which are inserted on the upper as well as on the lower jaw. 

 The interopercular is tracker-like and connects the back of the mandible with the opercular, 

 thus enabling the opercular flap to move with the mandible rather than with the branchial 

 arches. The point of attachment of the interopercular to the opercular is shifted dorsad, 

 perhaps to lessen the movement of the opercular when the jaw opens. 



Aleutera scfipta 



Fig. 163. Altutera scripta. 



Immediately behind the opercular is a toughened patch of skin, which I have called 

 the "tympanum." This is connected with the swim-bladder, with the rod-like post- 

 clavicle and the supraclavicle. It would not be surprising if this tympanum should serve 

 to transmit either sound waves or pressure reactions along the supraclavicle to the back of 

 the otic capsule. 



The elaborate apparatus that includes the "trigger" or erectile spine is well shown in 

 Figure 162. The erector muscles of the trigger run forward on the cranial roof and in 

 Aleutera (Fig. 163) the entire apparatus is connected with the skull roof so that a new 

 supraoccipital crest is rising. 



The dissections also suggest why the occiput of Balistes should be so strongly braced 



