GENERAL STRUCTURE. 



a cap of enamel underlain by dentine and supported on bone. 

 Allied to these are the calcined scutes of the Coffer-fishes (Os- 

 tracion), File-fishes {Batistes), and Sturgeons {Acipenser), to all 

 of which structures the term placoid scales was formerly applied. 

 A characteristic feature in the Teleostei is the 

 presence of a series of perforated scales run- 

 ning along the side of the body, known as the 

 lateral line, the canal of this line being apparently 

 in part connected with the supply of mucus, and 

 acting partly as a sense-organ. The modified 

 scales of this line may be larger or smaller than 

 those of the rest of the body, or may be the only Fi 

 ones present. A lateral line is also found in some 

 Ganoids and in certain Elasmobranchs, as well as in the Chimer- 

 oids. A series of large V-shaped scales found on the borders of the 

 fins of many Ganoids are termed fulcra. The dermal fin-rays are 

 peculiar to the present class, and are shown in figs. 836, 837. They 



Ganoid scale. 



Fig. 836. — Reduced left lateral view of the skeleton of the Perch {Pcrca). a, Premaxilla ; b, 

 Maxilla; c, Mandible; d, Orbit; e, Supraoccipital ; f, Preoperculum; g,g', Vertebra?; h, Pec- 

 toral fin ; i, Pelvic do. ; k, I, First and second dorsal do. ; in, Anal do. ; n, ri , Caudal do. The 

 bones between k and I and the vertebrae are the interspinals. 



occur both in the paired pectoral and pelvic fins, and also in the 

 median dorsal, caudal, and anal fins. In Elasmobranchs these fin- 

 rays are horny; but in the Teleostei (fig. 836) they are bony, and 

 generally split up into filaments at the extremities (/), although they 

 may be pointed (k). In Teleostei they generally consist of two 

 closely applied parts, diverging at the base to articulate in the 

 median fins with the interspinous bones of the endoskeleton, and 

 in the paired fins with the distal limb bones. In Elasmobranchs 

 the interspinals are represented by the so-called radial cartilages 

 belonging to the true endoskeleton. 



In Teleosteans and Ganoids the anterior rays of the dorsal and 



