364 MANUAL OF ZOOLOGY. 



The caudal vertebrae (fig. 133) have no marked transverse pro- 

 cesses ; but, in addition to the neural arches and spines, they 

 give off an inferior or hmmal arch below the body of the verte- 

 bra, and the haemal arches carry inferior spinous processes 

 (haemal spines). 



The ribs of a bony fish are attached to the transverse pro- 

 cesses, or to the bodies of the abdominal vertebrae, in the form 

 of slender curved bones which articulate with no more than 

 one vertebra each, and that only at a single point. Unlike the 

 ribs of the higher Vertebrates, the ribs do not enclose a thoracic 

 cavity, but are simply embedded in the muscles which bound 

 the abdomen. . Usually each rib gives off a spine-like bone, 



Fiff. 133. — Skeleton of the common Perch {J'erca fiuviaiiUs). p One of the pectoral 

 fins : V One of the ventral fins ; a Anal fin, supported upon interspinous bones (i) ; c 

 Caudal fin ; d First dorsal fin : d' Second dorsal fin, both supported upon interspmbus 

 bones; z/ Interspinous bones ; rRibs; j'Spinous processes of vertebrEe ; h Haemal 

 processes of vertebra. 



which is directed backwards amongst the muscles. Inferiorly 

 the extremities of the ribs are free, or are rarely united to der- 

 mal ossifications in the middle line of the abdomen ; but there 

 is never any breast-bone or sternitm properly so called. 



The only remaining bones connected with the skeleton of 

 the trunk are the so-called interspinous bones (fig. 133, ii). 

 These form a series of dagger-shaped bones plunged in the 

 middle line of the body between the great lateral muscles 

 which make up the greater part of the body of a fish. The 

 internal ends or points of the interspinous bones are attached 

 by ligament to the spinous processes of the vertebrae ; whilst 

 to their outer ends are articulated the "rays" of the so called 

 " median " fins, which will be hereafter described. As a rule, 

 there is only one interspinous bone to each spinous process, 

 but in the Flat-fishes (Sole, Turbot, &c.) there are two. 



