245 



sory ribs (intermuscular bones) have been 

 rotated forwards so that their exact length 

 may be indicated. The dotted line shows 

 the extent of the asymmetry. 



Fig. 11. The eighth trunk vertebra viewed from the 

 front of a 64cm. Plaice. Natural size. The 

 accessory ribs have been rotated forwards in 

 order to introduce their full length. The 

 dotted line shows the departure from the 

 symmetry. 



Fig. 12. The twelfth trunk vertebra of a 52cm. Plaice 

 seen in optical longitudinal section, the 

 ocular or right half of the centrum and right 

 neural arch having been ground away. 

 Natural size. The figure illustrates the 

 amphicoelous character of the centrum, and 

 the shape and extent of the notochordal 

 spaces. 



Fig. 13. The fourteenth or first caudal vertebra of a 

 52cm. Plaice seen from the front. Natural 

 size. The dotted line indicates the depar- 

 ture from the symmetry. The same ver- 

 tebra is shown in side view in fig. 18. 



Fig. 14. Moist dissection from right side of caudal fin 

 and termination of vertebral column of a 

 34cm. Plaice. Natural size. The fin rays 

 have been disarticulated from the fibro- 

 cartilaginous pad. 



Fig. 15. Dissection from right side of posterior extremity 

 of notochord and caudal fin supports of a 

 young Plaice of 17mm. Drawn with 

 camera, x 15. Notochord as yet unossified, 

 but faint vertebral constrictions (6 shown in 

 fig.) have appeared. The neural and haemal 



