224 



Dr. A. Giinther on Ceratodus, 



sistent, the lateral branches being either entirely absent (as in 

 the former), or quite rudimentary (as in the latter). In all these 

 cases the analogy of this structure to the diphyocercy of the 

 tenninal portion of the tail is apparent, whilst a heterocercal 

 condition is represented in the pectoral fin of Acipenser. In 

 this fish the axis {h) is not inserted in the longitudinal median 



Ceratodus, Acipcnser. 



a, carpal cartilage ; 5, jointed axis ; c, branches having the carpus as base ; 

 d, branches having the axis as base. 



line of the carpus («), but quite at the inner corner; conse- 

 quently branches exist on one side of the axis only, viz. on 

 that side on which they are needed for the support of the fin- 

 rays. The axis is comparatively short and feeble, composed 

 of three joints, and forming the base for three branches (d). 

 Three other branches (c) are inserted immediately into the 



