PROFESSOR OWEN, ON THE RHYNCHOSAURUS. 367 



so distinctly grooved as in the fine-grained slab, and the proximal extre- 

 mities of two long bones, which most resemble a lizard's radius and 

 idna. The shaft of the radius is more slender than that of the ulna: 

 one side is flat, the other convex : it expands and assumes a sub- 

 trihedral figure, by the development of a slight longitudinal ridge : its 

 proximal end is compressed and more suddenly expanded : its breadth 

 is 2| lines ; that of the shaft of the bone is 1 line. The impression, partly 

 broken away in the stone, indicates the greater expansion of the distal 

 end of this bone, with a length of 1 inch 3 lines. The proximal end of 

 the ulna has a distinct trihedral figure, and the expanded extremity is 

 produced backwards, so as to indicate the olecranon : the breadth of the 

 head is 4 lines ; that of the middle of the shaft is 1\ lines. There is a 

 portion of a broad and flat bone in this piece which may have belonged 

 to the scapular arch. 



Ilium. — In another piece of stone, with the other portion of the same 

 chain of five vertebras, there is a broad flat bone, apparently terminating 

 in a long narrow process at one end, which may be an ilium : its length 

 is indicated to be at least 1 inch 7 lines. 



Femora. — A thin piece of burr, or coarse-grained sandstone, contains 

 the articular end of a broad and flat bone, in which the raised oblong 

 surface of the joint is divided by a smooth channel, and may be compared 

 with the cotyloid portion of the ilium : the same piece of stone contains 

 the shafts of two long bones, most probably femora. The length of the 

 most perfect of these is two inches, and this does not include the distal 

 end : the diameter of the middle of the 6haft is %\ lines : the surface of 

 the preserved middle part shows the shaft to have been somewha.t angular : 

 the compact outer wall of the bone is about a quarter of a line thick : 

 a large medullary cavity extends the whole length of the shaft, agreeing 

 with the indications of terrestrial habits yielded by the bones before de- 

 scribed : the extremities of the femora are spongy, but much decomposed 

 and stained with iron-mould. 



There are few genera of extinct reptiles of which it is more desirable 

 to obtain the means of determining the precise modifications of the loco- 

 motive extremities than the Rhynchosaurus. The fortunate preservation 



s s 2 



