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. 248.) The bone of the tongue, Z, is 

 continued backwards by a series of pieces on the central line ; 

 and is articulated on each side witli a lateral branch of great 

 length and thickness, which, by its opposite extremity, is sus- 

 pended (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 9 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 ; then they curve upwards and inwards ; and at last 

 they are fixed to the base of the cranium by a series of small 

 connecting bones, ph, termed the superior pharyngeal. These 

 arches support the gills, and are thence called branchial arches. 

 Lastly, behind the last pair of these, at the entrance of the 

 oesophagus, are seen two inferior pharyngeal bones ; which are 

 usually so placed, as to apply themselves against the superior 

 pharyngeals just mentioned. 



522. Such is generally the complicated structure of the bony 

 head of Fishes. Some anomalies, however, are occasionally 

 observed ; 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 

 FIG. 249. SWORD-FISH. these fish as a powerful weapon 



to attack the largest marine ani- 

 mals. 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 there still exists much uncer- 

 tainty on this point: 



523. The vertebral column, which immediately follows the 

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



