SKELETON 



275 



are formed outside them in the now more superficial mesoblastic 



layers (Fig. 343). Only in the 



fatty or adipose fin of certain 



Teleostei (Salmonidae, Siluridae, 



etc.) do the actinotrichia acquire 



considerable size in the adult, and 



in these fins they form the sole 



organs of support. 



The skeleton of the paired 

 fins has already been discussed 

 above (p. 106), and will be further 

 dealt with below (p. 302) ; but 

 we may here consider the structure 

 of the limb-girdles. 



The endoskeletal pectoral 

 girdle consists of a bar of cartilage, 

 extending dorsally as the scapular . } nilt : r vie . w f *!" ri & ht , lialf f * he en , d - 



* - * skeletal pectoral girdle and tin of Salmo salar. 



region and ventrally as the cora- L. c, coracoid : a.c, distal cartilages of 



j /T:V ,,i \ mi radials ; nic, mesocoracoid arch; r. fifth 



COld region (-blgS. 2\-6). Ihe radial ; ,s scapula ; s./, scapular foramen. 



two halves do not fuse ventrally, 



and as a rule are widely separated, resting on the dermal covering 



bones (clavicle and cleithrum, p. 214). Among living Teleostomi 



Ventral view of the ]-lvic girdle and tins of ButfkenovttfOH Fwrili, Wht. : restored. The 

 skeleton of the right fin is completely exposed, o, jointed axis. (From Qtm.rt. Jvurn. Micr. 

 Sci.) 



