J. K. Tliaeher — Median and Paired. Fins. 295 



the rays. It is divided into three parts, Propterygium, Mesoptery- 

 gium and Meta])terygium. Each of tliese consists of a basale, vvliich 

 articulates Avith the shoulder girdle, and a number of rays set on its 

 edge. 



The fin of Protopteriis is derived from this by the destruction of the 

 pro- and mesopterygium. The metapterygiiim is hei'e represented by 

 the long articulated rod, Avhich alone remains in Liepidosiren paradoxa . 

 The row of cartilages along its sides are the metapterygial rays. 



In the Ganoids, Polypterns alone has the three divisions repi'e- 

 sented. In this, neither metapterygium nor propterygium bears rays. 

 These are confined to the mesopterygium, which is excluded from the 

 articulation with the shoulder girdle. 



In the other Ganoids the propterygium fails. Between the mesop- 

 terygium and metapterygium a number of rays are brought into 

 articulation with the shoulder girdle, resembling what is seen in some 

 of the Rays. 



The Teleosts in the main resemble this second group of Ganoids. 



The chiropterygium is derived from the metapterygium alone, and 

 thus resembles the limb of Protopterus. The fore limb will serve as 

 an example. The Stammreihe or hasale nietapterygii is presented 

 by the humerus, radius, radiale, carpale radii, the metacarpal and 

 phalanges of the thumb. The other bones are the rays belonging to 

 this, and their arrangement will be best understood by looking at the 

 Ichthyosaurtis limb, fig. 70. In 1870,* Gegenbaur published his 

 explanation of the liml) of the Enaliosaurs. The unbroken lines in 

 fig. 70 of Ichthyosaurus exhibit his view of the relations of the fin 

 with that of fishes. This may be regarded as closing the first stage 

 of the development of the theory in Gegenbaur's publications. 



The second immediately opens. For in the next numberf of the 

 Jena Zeitschrift there appears an extended article on the ventral fins 

 of Elasmobranchs. The pre\'ious view is modified as follows. The 

 fin-skeleton of the latest common ancestors of all Gnathostomes, is 

 represented pure and simple in the fore limb oi Protopterus a nnectens^ 

 and with only slight modification in the ventral fins of Elasmobranchs. 

 It now has a name given to it. It is called archipterygium. There 

 is a limb gii-dle, complete ventrad. On each side is articulated to this 



* Jenaische Zeitschr., Bd. v, Hft. .S. Gegenbaur, Ueber das Gliedmaassenskelet 

 der Enaliosaurier, Feb., 1870. 



f.Ten. Zeitschr., Bd. v, Hft. 4. Gegenbaur, Ueber der Gliedmaassen der Wirbel- 

 thiere im AUgemeinen und der Hintergliedraaassen der Selachier insbesondere, May, 

 1870. 



