THE SKULL 01' OSSEOUS FISHES. 1'23 



common undivided embryonal bud, wLicli is permanently typified in 

 the Lepidosii'cn. Since, however, in all its modifications, the anterior 

 or pectoral member is essentially, in its widest homological relations, 

 but the diverging or radiated appendage of the hasmal arch of the 

 occipital vertebra, we must not be surprised to find that arch retained, 

 as in the Synbranchi and Mura3nai, where no vestige of its appendage 

 is developed. 



To the inner side of the upper end of the coracoid there is attached, 

 in the Cod and Carp, a bony appendage in the form of a single styli- 

 form rib ; but in other fishes this is more frequently composed of two 

 pieces, as in the Perch. This single or double bone, here called 

 epi-coracoid {Jigs. 19. 40. 5s), is slightly expanded at its upper 

 end in the Cod-tribe, whei'e it is attached by ligament to the inner 

 side of the angular process of the coracoid : its slender pointed 

 portion extends downwards and backwards, and terminates freely in 

 the lateral mass of muscles. In its mode of attachment to the cora- 

 coid it resembles that of the hyoidean arch to the tympanic pedicle : 

 but in the Batrachus its upper extremity rises above the coracoid, 

 and is directly attached to the spinous process of the atlas. In some 

 fishes, as the Snipe-fish ( Centriscus Scolopax), the Cock-fish {Argy- 

 reiosus Vomer), the Lancet-fish (Siganus), it is joined by the lower 

 end to the corresponding bone of the opposite side, thus completing 

 an independent inverted arch, behind the scapular arch. There is 

 some reason, therefore, for viewing the epi-coracoids as representing 

 the inverted arch of the atlas, or its haemapopliysial portion, and not 

 as parts or appendages of a cranial vertebra. 



The usually free lower extremities of the epi-coracoids, together with 

 their taking no share in the direct support of the pectoral fin, and 

 their inconstant existence, oppose more strongly the view of their 

 special homology with the coracoids of higher Vertebrates. Tliey 

 have been regarded as advanced ' ossa innominata' by Cams 

 (xxxiv. p. 125.). To their special homology with the ' clavicles' of 

 higher classes it has been objected that these bones are always si- 

 tuated in those classes in advance of the coracoids ; but this inverted 

 position may be a consequence of the baclcAvard displacement of the 

 scapulo-coracoid arch in the air-breathing Vertebrata ; and if, not- 

 withstanding sucli displacement, we are able to discern the general 

 homological relations of that arch as the haemal one of the occipital 

 vertebra, we may, in like manner, discern in the clavicle a less dis- 

 placed haemal arch of the atlantal vertebra. 



The epi-coracoids are either absent or are very slender spines in 

 the Wolf-fish (Anarhickas), the Mullet, the Goby, the Stickleback, 



