284 



TRANSACTIONS OF THE AMERICAN PHILOSOPHICAL SOCIETY 



Balistids. — It may be an advantage for a nibbling fish to have its eyes as far back as 

 possible from the tip of the pincer-like mouth. At any rate, in Balistes (Figs. 161, 162) 

 the posterior border of the orbits is almost flush with the occiput and practically on top 

 of the pterotic and hyomandibular- socket. This fact, together with the extreme forward 



M.protrac+or carlngB 



Vfyl.deprssso 



M.lewator^^ lateralis 

 -percuK \ \ ' 



M.depre^^or 

 P.t^'y^" Mm.sDinales 



IVl.errector.i, 

 pterygii 



Fronfel 

 M.adcLmand.supv- 



Metier "-^ 

 fVe+rontal 



M.add.mand.&upi- 



De+h V""\"' 



pmx 



Max 



Interop- f 



M.add.mand 

 prof. 



InleWiyal \ 



showing throo^h • Posicb^. Mpno+rac+or pelvis 



lnWpli5an,e.t ^^^.^^^^ 



Fig. 162. Balistes sp. 



prolongation of the suspensorium, results in some anomalous topographic reversals of 

 primitive conditions, especially in Aleutera (Fig. 163): the posterior process of the pterotic 

 now points downward and forward instead of backward; the pedicel for the opercular on 

 the hyomandibular also points forward and downward and the hyomandibular itself points 

 almost forward. Meanwhile the preorbital part of the parasphenoid has developed a great 

 median keel which cooperates with the elongated and well-stiffened mesethmoid to form 

 the base for the upper jaw. The opercular series, already restricted in Xesurus, has lost 

 further territory in the balistids. 



A dissection of Balistes (Fig. 162) reveals many interesting relations between the 

 skeleton and the soft parts by which it is moulded. The adductor mandibulae muscles 



