58 



ORGANS OF SUPPORT, 



diagram (Fig. 28,) where A shows their most common 

 positions with relation to each other in the caudal por- 

 tion of the skeleton of an osseous fish where they are de- 

 signed to give great extension for the attachment of the 

 powerful lateral muscles which move the tail. The body 

 of the vertebra, or cyclo-vertebral element (a,) supports 

 the two superior laminae or peri- vertebral elements (b, b,) 

 which early unite above to form the small foramer for 

 the spiral cord (e) ; and beyond their termination we 

 observe the interspinous bone (c,) and the ray (d,) of the 



FIG. 28. 



external fin, which are the two epi-vertebral elements 

 placed in a vertical line. The analogous elements are 

 seen on the lower part of the vertebra, where the two 

 inferior laminae (/,/,) or para-vertebral elements, form a 

 larger foramen for the lodgment of the great continua- 

 tion of the aorta (i,) above, and the vena cava (&,) below. 

 The inferior interspinous bone (g,) and the ray (h,) of 

 the external fin, are the two cata-vertebral elements placed 

 in a vertical line, like the epi-vertebrals above. These 

 vertebral elements often assume, in the region of the 

 abdomen in fishes, the position marked in the diagram 

 B, of Fig. 28, where the superior elements remain as in 

 Fig. A, but the inferior laminae (/,/,) or para-vertebrals, 

 are stretched out in a horizontal direction, and have the 

 two cata-vertebrals (g,y,) extended from their ends in 



