The Skeleton of the Fish 



51 



60'/ 



Fig. 35. — Inner view of 

 shovilder-girdle of the 

 Buffalo - fish, Ictiobus 

 buhalus Rafinesque, 



showing the mesocora- 

 coid(.59). (After Starks.) 



fowl. Behind the base of the clavicle, the sword-shaped post- 

 clavicle (56) extends downward through the muscles behind the 

 base of the pectoral fin. In some fishes, 

 as the stickleback and the trumpet-fish, a 

 pair of flattish or elongate bones called 

 interclavicles {injraclavicles) lie between 

 and behind the lower part of the clavicle. 

 These are not found in most fishes and 

 are wanting in the striped bass. They are 

 probably in all cases merely extensions of 

 the hypocoracoid. 



Two flat bones side by side lie at the 

 base of the pectoral fin, their anterior edges 

 against the upper part of the clavicle. 

 These are the liypcrcoracoid (57), above, 

 and hypocoracoid {^?,),he\o\N. These have 

 been variously called scapula, coracoid, 

 humerus, radius, and ulna, but being found 

 in the higher fishes only and not in the 

 higher vertebrates, they should receive 

 names not used for other structures. The hypercoracoid is 

 usually pierced by a round foramen or fenestra, but in some 

 fishes (cods, weavers) the fenestra is between the two bones. 

 Attached to the hypercoracoid in the striped bass are four 

 little bones shaped like an hour-glass. These are the actinosts 

 (160) (carpals or pterygials), which support the rays of the pec- 

 toral fin (61). In most bony fishes these are placed much as 

 in the striped bass, but in certain specialized or aberrant forms 

 their form and position are greatly altered. 



In the anglers (Pedicidati) the " carpals " are much elongated, 

 forming a kind of arm, by which the fish can execute a motion 

 not unlike walking. 



In the Alaska blackfish (Dtillia pectoralis) the two cora- 

 coids are represented by a thin, cartilaginous plate, imper- 

 fectly divided, and there are no actinosts. In almost all bony 

 fishes, however, these bones are well differentiated and distinct. 

 In most of the soft-rayed fishes an additional V-shaped bone 

 or arch exists on the inner surface of the shoulder-girdle near 

 the insertion of the hypercoracoid. This is known as the meso- 



