SKELETON. 53 



The vertebrEe are either abdominal or caudal vertebrae, 

 the coalescence of the parapophyses into a complete hsemal 

 ring, and the suspension of the anal fin generally forming a 

 sufficiently well-marked boundary between abdominal and 

 caudal regions (Fig. 23). In the Perch there are twenty- 

 one abdominal and as many caudal vertebrae. The centrum 

 of the first vertebra or atlas is very short, with the apo- 

 physes scarcely indicated, and lacking ribs like the succeediug 

 vertebra. All the other abdominal vertebrae, with the ex- 

 ception of the last or two last, are provided with ribs, many 

 of which are bifid (72). A series of flat spines (74), called 

 interneurals, to which the spines and rays of the dorsal 

 fins are articulated, are supported by the neural spines, the 

 strength of the neurals and interneurals corresponding to 

 that of the dermal spines (75). The caudal vertebrae 

 differ from the abdominal in haviiig the haemapophyseal 

 elements converted into spines similar to the neurals, the 

 anterior being likewise destined to support a series . of 

 interhcemals (79), to which the anal rays are articulated. 

 The last and smallest caudal vertebra articulates with the 

 hypural (70), a fan-Like bone, which, together with the dilated 

 hindmost neural and haemal elements, supports the caudal 

 rays. 



Looking at a perch's skull from the side (Fig. 24), the 

 most superficial bones will be found to be those of the jaws, 

 a chain of thin bones round the lower half of the eye, and the 

 opercles. 



The anterior margin of the upper jaw is formed by the 

 intermaxillary or premaxillary (17) which bears teeth, ter- 

 minates in a pedicle above, to allow of a forward sliding motion 

 of the jaw, and is dilated into a flat triangular process behind, 

 on which leans the second' bone of the upper jaw, the max- 

 illary (18). This bone is toothless, articulates with the vomer 

 and palatine bone, and is greatly dilated towards its distal 



