6 BONES OF THE HEAD OF FISHES. 



which serves for the support and protection of the gills, and 

 which appears to resemble the hyoid bone of higher animals 

 enormously developed. (Fig. 348.) The bone of the tongue, /, 

 is continued backwards by a series of pieces on the central 

 line ; and is articulated on each side with a lateral branch of 

 great length and thickness, which, by its opposite extremity, 

 is suspended (as it were) to the internal face of the before- 

 mentioned partition. These lateral branches, formed of several 

 bones, carry at their lower border a series of flattened rays, 

 r, r, curved backwards, which unite with the opercular bones 

 to complete the walls of the branchial cavities, and which 

 are known under the name of branchio-stegal rays. Behind 

 these branches we meet with four pairs of bony arches, a, 

 passing off from the central portion of the hyoid apparatus. 

 These are first directed backwards ; they then curve upwards 

 and inwards, and are at last fixed to the base of the cranium 

 by a series of small bones, ph, termed the superior pharyngeal. 

 These arches support the gills, and are thence called branchial 

 arches. Lastly, at the entrance of the resophagus, are seen 

 two inferior pharyngeal bones ; which are usually so placed, 

 as to apply themselves against the superior pharyngeal just 

 mentioned. 



542. Such is generally the complicated structure of the bony 

 head of Fishes. Some anomalies, however, are occasionally ob- 

 served; thus amongst the Sword-fishes and some other allied 



species of Tunny, the upper jaw is 

 prolonged, so as to constitute a kind 

 of beak, like a spit or the blade of a 

 sword : which serves these fish as a 



TIG. 349. SWORD-FISH. 



powerful weapon to attack the larg- 

 est marine animals. We shall not dwell here on the comparison of 

 the different pieces of which the head of Fishes is composed, with 

 the bones of the head of the Mammalia ; as some points connected 

 with this subject must still be regarded as uncertain ; and the de- 

 tails necessary to render it intelligible would lead us too far. 



543. The vertebral column, which immediately follows the 

 head, only presents two distinct portions, the one dorsal, the 



