:g6 
ERIK A : SON STENSIO 
skeleton of the ventral fins in the sturgeons is primitive, even more primitive than in 
the Elasmobranchs. The skeletal element that v. Rautenfeld called the «Basalplatte» is 
termed by him, as already mentioned above, the «vorderstes (proximales) Basale», and 
he believed that he had also discovered that this skeletal element not only corresponded 
to a basale propterygii but that it also comprised the pelvis and the most anterior part 
of the basale metapterygii. «Kurz», he writes (p. 71), «es handelt sich bei jener Knorpel- 
platte gleichsam noch um einen indifferenten, basipterygealen Mutterboden, in welchem 
in der Regel auch noch das Becken latent bleibt. In manchen Fallen aber gliedert sich 
dasselbe mehr Oder weniger vollkommen ab, verbindet sich in Form einer primitiven 
Symphyse und unter mehr Oder weniger vollkommener Verknocherung, resp. Verkalkung 
mit seinem Gegenstiick.» The cartilaginous elements (the free basal segments of 
v. Rautenfeld’s description) following behind this most anterior basale together form, 
according to Wiedersheim’s view, a polymerous metapterygeal axis. 
In order to explain the skeleton the ventral fins in Polypterus, Amia, Lepidosteus 
and Teleosts Wiedersheim starts out from the conditions in the sturgeons. The skeletal 
element of Polypterus, Amia, Lepidosteus and Teleosts termed by v. Davidoff the basale 
metapterygii is taken by him to be homologous with the «vorderstes Basale» of the 
sturgeons, if the pelvic part of this «Basale» was excluded. In the Teleosts, however, 
the «Basale» is said to include also the complex of endoskeletal radials situated distally 
of it in sturgeons and other ganoids. In Polypterus he thought, like Thompson (i§86, 
p. 534), he could discover an equivalent to the pelvis in the paired or unpaired little piece 
of cartilage between the anterior ends of the «vorderstes Basale» of either side. In Amia, 
Lepidosteus and Teleosts, on the other hand, a pelvic element or a pelvic part would be 
absent. The absence of the pelvis in these forms he was of course inclined to take to be 
most probably primary, i. e. the higher Ganoids and the Teleosts would originate from 
forms in which a pelvis was not yet developed. On the other hand he emphasizes, how¬ 
ever, that the possibility must also be taken into consideration of the pelvis being reduced. 
Mollier (i 8 g 3 , p. 121 —128; 1897, pp. 53 — 60) has in his general considerations of 
the paired extremities of the vertebrates also dealt with the ventral fins of the sturgeons. 
He states that all the endoskeletal radials of either of the ventral fins in Polyodon 
sometimes articulate with a large plate, which, in accordance with the results that he 
considered he had attained with regard to the fin skeleton in general, he called the 
primary basal. This large primary basal he considers to comprise, if I interpret his 
account correctly, the homologues of the basale pro- and basale metapterygii and parts 
of the pelvic girdle as well. On the other hand in the cases when a skeletal plate 
towards which radials articulate is present only in the anterior part of the endoskeleton, 
he holds the posterior part of the primary basal to be partly reduced and this inter¬ 
pretation of the conditions is maintained by him for sturgeons in general, thus approach¬ 
ing rather near to Wiedersheim’s view with regard to the interpretation of the elements 
of the fin skeleton. Contrary to Wiedersheim, however, he upholds the view that the 
inner skeleton in the ventral fins of the sturgeons must be considered to be strongly 
reduced, a conclusion to which Gegenbaur, v. Rautenfeld and Emery (1894) also arrived. 
Like Gegenbaur he too states, contrary to Wiedersheim, that the same must be the case 
with the endoskeleton in the corresponding fins in Polypterus. 
