2 STEUCTUEE OF IHE PAIRED FIXS OF CERATODUS, 



PAPERS READ. 



On the Structure of the Paired Fins of Geratodus, 



WITH remarks on the GENERAL THEORY OF THE 



Vertebrate Limb. 

 By William A. Haswell, M.A., B.Sc. 



[Plate I.] 



In his description o£ Ceratodus JForsferi,'-^ Dr. Griintlier says 

 respecting tlie fins : 



" Tlie limbs consist of two pairs of paddles similar in appear- 

 ance to the termination of the tail ; viz., a longitudinal axis, 

 formed by the endoskeleton and muscles and covered with scales 

 is surrounded by a broad rayed fringe. These paddles are 

 structurally identical with the fins of Lepidosiren : only the axis 

 and also the fringe are much dilated. 



"The paddle is joined to the scapular arch by an elongate 

 flattish, slightly curved cartilage ; its proximal end has a glenoid 

 cavity fitting into the humeral condyle ; the joint is simple, free, 

 allowing of a considerable amount of motion, its parts being held 

 together by a ligament fastened around its circumference. This 

 is the only true joint in the limb, all the other parts being fixed 

 to one another by connective tissue. I consider this cartilage to 

 be the forea-rm ; a horizontal section along its longitudinal axis 

 does not shew any primary division. The next following cartilage 

 forms the base of the paddle ; although externally it appears as 

 a single flat broad short piece, unevennesses of its surface indicate 

 that several primary pieces are coalesced in it." 



" I am confirmed in this view by a horizontal section, in which 

 the lines of the former divisions are preserved in the shape of 

 tracts of a white connective tissue. Three such divisions may be 

 distinguished corresponding to the three carpals of most Plagios- 

 tomes. If this determination is correct, then the antibrachial 



* Phil. Trans. 1871. 



