FISH IN GENERAL. 63 



chaetodons, are clavate. Some genera, chiefly scombri, have 

 the spinous parts of the anterior dorsal without membrane, 

 and more often still the posterior rays of the back and anal 

 fins are separated, and form false fins. Many fish have no 

 sternum. When found, it consists of a series of single bones, 

 at which the ribs terminate, as may be seen in herrings and 

 vomers. 



The bones of the shoulder and arm are found immediately 

 behind the orifice of the gills, and consist of a series forming 

 a kind of frame, into which the operculum shuts when closed. 

 The two series usually attached to the head above, and 

 uniting together below, form an osseous belt, encircling the 

 body : their inferior symphysis, united by ligaments with the 

 tail of the hyoid bone (No. 42), assists it in forming the 

 isthmus which separates the external opening of the gills 

 beneath. This belt, as in eels, is sometimes free. When the 

 series is complete, three bones are found in each half: the 

 uppermost (No. 46) is forked, and is in part visible in the form 

 of a large scale, often serrated at the opening of the gills ; the 

 next (No. 47) is sometimes wanting, and the third (No. 48), 

 always the largest, terminates as above stated ; a fourth and 

 fifth bone (No. 51 and 52) adhere to the inner surface, above 

 each other, each pierced or scolloped out. On the free side the 

 pectoral fin is placed, by means of four or five intermediate 

 bonelets (No. 53) seated between the two bones and the rays 

 of the fin, with the exception of the first ray, which is con- 

 nected with the superior bone (No. 52). These bonelets 

 represent the carpal series, and if this opinion be admitted, 

 the two other bones (No. 51 and 52) will be the ulna and 

 radius ; thus also the great bone of the girdle which sup- 

 ports the two others may be regarded as the humerus, and 

 the first and second (No. 46 and 47) will represent the shoul- 

 der blade. Therefore these pieces will require the names of 

 supra-scapular, scapular, humeral, ulnar or cubital, and radial. 



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