57 



baseost and axonost is a very slight non-ligamentous one, 

 and hence the fin ray and baseost are only held down in 

 the soft cartilage cup at the head of the axonost by the 

 elevator and depressor and right and left abductor muscles 

 [F.R. e) of the fin ray. The result is that the fin ray and 

 baseost are capable of being moved on the axonost in any 

 direction. The axonosts are held in position by two liga- 

 ments : (a) by a longitudinal vertical ligament which 

 keeps the axonosts at their correct distances from each 

 other and separates the right and left series of the fin-ray 

 muscles ; (h) by transverse ligaments [Ax. a) which keep 

 the axonost from moving from side to side. The head of 

 the axonost contains a triangular plug of typical hyaline 

 cartilage [Ax. b) as before mentioned. The whole appa- 

 ratus is somewhat asymmetrical as shown in the figure. 



The attached table, based on the examination of a 

 52cm. plaice, has been drawn up to show the number, 

 position, and precise relations of the ribs, neural and 

 haemal spines, and skeleton of the dorsal and anal fins. 

 The specimen had 42 vertebrae (cp. figs. 17, 18 and 19). 

 The division into regions is somewhat arbitrary, since for 

 example the boundary between the cranial and occipital 

 regions is along the axis of fin ray 9 and baseost 8, i.e., 

 betiveen axonosts 8 and 9. In the anal fin the axonosts 1 

 to 7 are situated morphologically between vertebrae 13 and 

 14 (cp. fig. 18), and hence at this region (as 

 indicated by the line) the correspondence between the two 

 regions of the table has no morphological value. Behind 

 this ambiguous region [i.e., behind and including 

 vertebrae 14) it will be noticed that although there is a 

 very wide disagreement in the disposition of the fin skele- 

 ton above and below the vertebral column, yet the 

 numbers of the fin rays are practically the same, i.e., 45 in 



