54. PROCEEDINGS OF THE GEOLOGICAL SOCIETY.
(fig. 8), is, I suggest, neither " the apophysial lever of the fibula," nor
" the calcaneum," nor yet " a detached olecranon," but it is the fibula
Pig. 8. — End of Femur, Epipodial and Tarsal Bones of Pliosaurus
portlandicus, Owen. (From a plate in the 'Fossil Keptilia.')
T, the tibia=66, tibia, Ow. ; 67, the intermedium = fibula, Ow. ; 67', the fibula=
fabella, Ow.; t, os tibiale ; c l , c 2 , ossa centralia.
itself; and the ossicle marked 67 in the same figure is not the fibula,
as its number would imply, but it is the intermedium. In the dia-
gram fig. 7 (copied from fig. 3 in pi. xli. vol. xxv. Quart. Journ.
Geol. Soc. 1870), which represents the paddle of Plesiosaurus
Manseli, the letter T marks the tibia ( = 66 Owen), i denotes
the intermedium ( = 67 Owen), and F the fibula ( = 67' Owen). I
imagine that the identity of these three elements in the epipodial
segment of the above two paddles is unquestionable, and also that
their identity with the three epipodial elements in the paddle of
Sauranodon figured by 0. C. Marsh is beyond doubt (fig. 9). I
think also that the homology of the two laterally placed ossicles in
the epipodium of Sauranodon with the two similarly situated ossicles
in the epipodium of Ichthyosaurus (fig. 10) cannot be disputed. But
these latter are by general consent the homologues of the tibia and
fibula of higher vertebrates. It follows, therefore, that the lateral
ossicles in the epipodium of Pliosaurus portlandicus (66, 67') and
in that of Plesiosaurus Manseli (T, F) are also the tibia and fibula.
Now the middle ossicle in the epipodium of Sauranodon has been
identified by 0. C. Marsh, rightly as I think, with the intermedium,
the opinion at which I had myself arrived with respect to the cor-
responding element in Plesiosaiwus Manseli, though noticing its
agreement with the ossicle which in Ichthyosaurus is intercalated