SEA-FISHERIES LABORATORY. 359 



Inner median -flexor (i.m.e.) A very short muscle 

 arising from the endopleurite near the middle of the base 

 of the foramen. It passes downwards below the other 

 flexors and is inserted at the base of the scaphognathite 

 on the outer side of the inner flexor. 



The extensor muscles are situated beneath the flexors, 

 so that it is necessary to cut away the latter in order to 

 expose the extensors. There is one extensor corresponding 

 to each flexor, and the insertion of each extensor is near to 

 that of the corresponding flexor. All the extensors arise 

 at the base of the anterior face of the last cephalic 

 endopleurite. They are all short muscles, and are 

 inserted on the posterior wall of the base of the 

 scaphognathite. 



Inner extensor (i.f.) Arises at the base of the endo- 

 pleurite. It passes inwards and is inserted close to the 

 inner flexor. 



Inner median extensor (i. m.f.) It lies immediately 

 below the inner median flexor, and above the three other 

 extensors. It arises about the middle of the base of the 

 endopleurite and passes downwards and forwards. Its 

 insertion is close to that of the inner median flexor. 



Outer median extensor (p. m.f.) Its origin is on the 

 inner side of the previous muscle. It passes obliquely 

 outwards and forward beneath the previous muscle, and 

 is inserted close to the insertion of the outer median 

 flexor. 



Outer extensor (p.f) A very short and broad muscle 

 arising on the outer side of the origin of the inner 

 median extensor. It passes outwards and downwards and 

 is attached to the scaphognathite close to the insertion 

 of the outer flexor. 



The last two muscles have their insertions situated 

 in the thickened bulb-like portion of the scaphognathite. 



