HIGH SCHOOL ZOOLOGY. li) 



while the series of spines (to which the common name of 

 spine, spinal column, etc., for the verteV)ral column is due) 

 cliiefly serves for the attachment of muscles. In higher "Verte- 

 brates not only are the centra intimately united to each other, 

 but the arches have certain projections (articular processes), 

 forming joints with simihir processes on the arches in front and 

 behind. These are not very much, developed in the catfish, 

 but this moile of union permits a certain amount of rotary 

 movement between the vertebrae, to which the word vertebra 

 owes its origin. 



In all fishes there may be distinguished in the vertebral column 

 two regions, the trunk and the tail, the former extending as far 

 Hack as the crelom referred to above, the latter beliind that. 

 In addition to the neural arches and spines, the caudal vertebra; 

 have haemal arches and spines, which j)rotect the blood vessels 

 i-unning back through the tail below the centra, while the trunk 

 vertebrae have I'ibs which generally protect the contents of the 

 cceloui, but do not meet below nor carry spines. 



The ribs are not .articulated directly to the centra, but to projections 

 from them, transverse processes, which appear to be the real represent- 

 atives of the haemal arches. 



Some of the anterior trunk vertebrje in the catfish and 

 its allies are very different from the others, being modified in 

 connection with the oi-gan of hearing, and in all fishes the most 

 ])Osterior vertebrae are altered in connection with the tail. The 

 special way in which this alteration affects the catfish may be 

 seen in Fig. 5, tis far as appearance goes the rays of the caudal 

 fin seem to be equally divided above and below the end of the 

 vertebral column, (the fin is said to be homocercal), but in 

 reality the tip of the vertebral column turns abruptly upwai-ds 

 so that most of the rays are really on its ventral surface. We 

 shall see that in certain other fishes tliis uiicrpial di\asion of 

 the tail-fin is much more apparent (heterocercal). 



