|
forms merely a short stem or handle (as it may be
called) connected with the transverse clavicles ; whereas in the
plesiosaurus it is considerably more developed. The general
analogies between these parts in the reptile tribe, in the
ornithorynchus, and in birds, have been ably pointed out by Geoffrey
St. Hilaire and Cuvier.
In the plate containing a restoration of the plesiosaurus, I have
added for the purpose of comparison a sketch of this part in the
ichthyosaurus. That published in the Philosophical Transactions does
not exhibit the tripartite division of the furcula, and erroneously
makes its branches curve considerably too much upwards. The present
outline is founded on three very perfect specimens, which entirely
agree with one another in the parts here represented, and leave no
doubt of their actual form.
Extremities.-The humerus articulates immediately with the
bones which in my preceding descriptions I had considered as the
first row of the carpus ; which contains only two instead of the
three pieces placed together in the conjectural restoration. I have
again to acknowledge the error into which I have been led in the
insertion of a supposed radius and ulna between these parts; for the
two pieces which form the first row formerly ascribed to the carpus,
now appear to be the true representatives of the radius and ulna,
though greatly differing in form from the usual type of those
parts*.
All the paddles are composed of two rows of nearly circular or
discoidal bones, representing the carpus and tarsus, and of five
digitated series, representing the metacarpal or metatarsal and
phalangic bones (the distinction between these being inappreciable,
though we may of course in conformity to the usual nomenclature,
term the first phalangic bones metacarpal, &c., if so inclined.
The first or anterior digit on each paddle has four phalanges ; the
last seven. These are evidently complete in the specimen ; the whole
five digits stand as follow :
| Anterior paddle. |
Posterior paddle. |
| 1st digit, |
4 phalanges. |
1st digit, |
4 phalanges. |
| 2d .... |
7, and seems complete. |
2d .... |
8, complete. |
| 3d .... |
7, incomplete. |
3d .... |
10, ?uncertain whether |
| 4th .... |
6, incomplete. |
4th .... |
9, ?complete or not |
| 5th .... |
7, complete. |
5th .... |
7, complete |
This great multiplication of joints in the phalangic series
strongly di- |
| * The conjectural restoration of the paddles
would very nearly apply to the posterior paddles as exhibited in this
specimen, by abstracting the outer bone from this supposed carpus, and
removing also the exterior and circular bones from the edges of the
paddle as there drawn. F was led to introduce these exterior
paddle-bones from the specimen represented fig. 1, PI. XLII.,
Geological Transactions, Vol. V., in which they are so placed ; but I
have subsequently retracted this view having learnt that when the
specimen referred to was found, the bones in question were loose, and
had been subsequently glued into their present situation, in
consequence of a conjecture of the proprietor. I mention this
circumstance, lest any real inconsistency should be supposed to exist
between that specimen and the more perfect and illustrative remains
now discovered. |
