CHARACTERS OF FISHES. 



391 



seven of these on each side. Above the urohyal, and attached 

 in front of the body of the os hyoides, is a chain of bones, 

 placed one behind the other, and termed by Owen the "basi- 

 branchial bones." Springing from these are jour bony arches 

 the "branchial arches" which proceed upwards to be con- 

 nected superiorly by ligament with the under surface of the 

 skull. The branchial arches as will be subsequently de- 

 scribed carry the branchiae, and each is composed of two 



Fig. 164. Os hyoides, branchiostegal rays, and scapular arch of the Perch (after 

 Cuvier). j,s Supra-scapula ; j Scapula ; co Coracoid ', cl Supposed representative of 

 the clavicle ; a Glossohyal bone ; b Basihyal ; c Urohyal ; d Ceratohyal ; e Epihyal ; 

 f Stylohyal ; br Branchial arches ; t Branchiostegal rays. 



main pieces, termed respectively the " cerato-branchial " and 

 " epi-branchial " bones. The second and third arches are con- 

 nected with the skull by the intervention of two small bones, 

 often called the "superior pharyngeal bones," but termed 'by 

 Owen the " pharyngo-branchial " bones. 



The limbs of fishes depart considerably from the typical form 

 exhibited in the higher Vertebrates. One or both pairs of 

 limbs may be wanting, but when present the limbs are almost 



