OR OSSEOUS SYSTEM. 65 



and have been also regarded by some as elements of the 

 lower jaw. 



The arches, which hang down from the sides of the 

 vertebral column, are more like ribs in fishes than in 

 higher classes, as the lower jaw, the os hyoides, the sca- 

 pular arch, and that of the pelvis. The os hyoides is very 

 large here, as in all water-breathing vertebrata, from its 

 supporting the branchial arches ; it consists of five pairs 

 of pieces besides the body or lingual bone ; it is suspended 

 from the temporal bones, and it is chiefly by its motions 

 backwards and forwards that respiration is effected, not only 

 in fishes, but in amphibia and chelonia. It forms the 

 second arch below the head, between the arch formed by 

 the lower jaw, and that formed by the scapular and coracoid 

 bones. Its sides support the four pairs of branchial arches, 

 the analogues of tracheal rings, and its exterior gives at- 

 tachment to the branchiostegous rays of the opercular 

 membrane. 



The arms of fishes, or their pectoral fins are almost 

 always more developed than their legs, or ventral fins, and 

 they are generally attached to the back part of the skull, 

 by means of an osseous arch composed behind of the 

 two scapulse, and before of the two coracoid bones. In the 

 perch (Fig. 31.) the two highest or first portions of this 

 arch on each side (46, and 47,) are regarded as the scapulae, 

 the long angular bone (48, 48.) attached to these, as the 

 humerus, the two succeeding bones (51,52,) as the ulna 

 and the radius. To these succeed the bones of the carpus 

 (53,) and this member is terminated by the long and nu- 

 merous phalanges of the fingers. The small styliform ter- 

 mination (50,) of the scapular arch, composed sometimes 

 of one, and sometimes, as in the perch, of two pieces (49, 

 50,) is considered as the coracoid bone, and they occasion- 

 ally meet in front, as in higher oviparous classes, though 

 without the intervention of a sternum. The relative mag- 

 nitude of the arms of fishes, and their constancy, compared 

 with the posterior members, corresponds with their great 

 size in the embryo of higher classes, and their preceding 

 the legs in their development from the trunk. The posterior 

 members, the legs, or the ventral fins of fishes (80, 81, 82,) 

 are unconnected with the vertebral column, suspended from 



PART I. F 



