GADIFORMES 



479 



from three in Gadomus to six in Macrurus and ten in Muraenolepis. 

 This increase above the usual number, five, is probably secondary 

 (p. 404). The pelvic fins, which may have as many as twelve 

 dermal rays, are very far forward, anterior to the pectorals in the 



Diagrams of a transverse section through the front of the orbit A, of Gadus, B, of Perca, 

 to show the position of the olfactory nerves and tracts, b.c, brain-cavity of cranium ; c.s, 

 cartilaginous interorbital septum ; e.c, ethmoid cartilage ; o.n, olfactory nerve in B, olfactory 

 tract in A ; op, optic nerve ; s, membranous interorbital septum. 



Gadidae, but the girdle is only loosely attached to the cleithra. 

 Usually pleural ribs as well as epipleurals are present on the trunk 

 vertebrae, except the first two. 



Scales generally cover the head ; they are cycloid in the 



ha,. 



vl. hy. 



FIG. 500. 



Tail of n young Cod. (After A. Agassiz.) <i, dorsal cartilage (neural arch ?) ; <?./, lepidotrichia of 

 dorsal lob of caudal fin ; li.., haemal arch ; hy, hypural ; n.sp, neural spine ; ni, notochord. 



Gadidae and some Macruridae ; but in the latter family they 

 become spinous (Fig. 512, B). The air-bladder is closed, and the 

 pseudobranch usually sunk and glandular. Often a mental barbel 

 is present. The Gadiformes have not been found below the 

 Miocene and Oligocene rocks. 



