Fig. 35.—Inner view of shoulder-girdle of the Buffalo-fish, Ictiobus bubalus Rafinesque, showing the mesocoracoid (59). (After Starks.)

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 hypercoracoid (57), above, and hypocoracoid (58), below. 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 (60) (carpals or pterygials), which support the rays of the pectoral 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 (Pediculati) 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 (Dallia pectoralis) the two coracoids are represented by a thin, cartilaginous plate, imperfectly 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 mesocoracoid (59). It is not found in the striped bass, but is found in the carp, catfish, salmon, and all their allies.

Fig. 36.—Sargassum-fish, Pterophryne tumida (Osbeck). One of the Anglers. Family Antennariidæ.

Fig. 37.—Shoulder-girdle of Sebastolobus alascanus Gilbert. (After Starks.)