CLASS OSTEICHTHYES. BONY FISHES 



381 



Spinous dorsal fin Soft dorsal fin Caudal fin 



Premaxilla 

 Frontal 



Pectoral 

 Quadrat© girdle 

 Articular 



Maxilla 

 Dentary 



Pectoral fin 

 False rib 



Anal fin 

 Interspinous bones 



Figure 254. The skeleton of a fish (yellow perch). Note that the skeleton centers about the 

 vertebral column and skull. 



tively uniform in structure. Ribs are at- 

 tached by ligaments to the abdominal verte- 

 brae and serve as a protecting framework 

 for the body cavity and its contents. There 

 is no sternum. The skull consists of a large 

 number of parts— some bone, others car- 

 tilage. The visceral skeleton is composed of 

 7 paired arches more or less modified. The 

 first or mandibular arch forms the jaws. 

 The second or hyoid arch is modified as a 

 support for the gill covers. Arches 3 to 7 

 support the gills and are known as gill 

 arches. The first 4 bear spinelike ossifica- 

 tions, the gill rakers, which act as a sieve to 

 intercept solid particles and keep them away 

 from the gills. 



The appendicular skeleton is represented 

 in the perch by pectoral and pelvic girdles 

 and fins associated with them; and median 

 fins (Fig. 254). The pelvic girdle is not very 

 typical in form, being degenerate or pos- 

 sibly primitive. 



Muscular system 



The principal muscles are those used in 

 locomotion, respiration, and in obtaining 

 food. The movements of the body employed 

 in swimming are produced by 4 longitudinal 

 bands of muscles, one heavy band on each 

 side along the back, and a thinner band on 

 each side of both trunk and tail. These are 

 arranged in zigzag myotomes. Weaker mus- 

 cles move the gill arches, operculum, hyoid, 

 and jaws. 



Digestive system 



The aquatic insects, mollusks, and small 

 fishes that constitute a large part of the 

 food of the perch are captured by the jaws 

 and held by the many conical teeth. Teeth 

 are borne on the mandibles and premaxillae, 

 and on the roof of the mouth. They are not 

 used for chewing food, but only for holding 

 it. A rudimentary tongue projects from the 



