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THE LEG AND TOE BONES OF PTYCHOSIAGUM. 
By R. Broom, M.D., B.Sc. 
(Read November 28, 1900.) 
(Plate XXXIT.) 
Among a series of geological specimens recently presented by Mr. 
Leshe, of Port Elizabeth, to the Eastern Province Naturalists’ Society 
was a piece of stone on which were displayed a small tibia and 
fibula. The specimen had been sent from Colesberg and had been 
found in association with a fine skull of Ptychosiagum Murray, now 
in Mr. Leslie’s possession. As the matrix of the specimen is quite 
similar to that of the skull, and as the peculiarities of the leg bones 
are such as might be expected from what is known of the other limb 
bones of Ptychosiagum, there does not seem to be any reasonable 
doubt in referring the bones to the same genus. 
In clearing away the matrix from the bones I was fortunate in 
discovering the greater part of two toes with the bones in apposition, 
and a couple of carpal bones. 
The tibia is almost quite perfect. It is narrow and rounded in the 
middle, slightly expanded at the proximal end, and greatly expanded 
at the lower end. Down the front of the upper third of the bone 
there is a fairly well-marked crest, on the inner side of which the 
bone is slightly hollowed for the attachment of the tibialis anticus 
muscle. On the outer side of the upper part of the crest is a small 
depression, doubtless corresponding to that seen in a similar situation 
in the tibia of Ormthorhynchus. The lower end of the tibia is so 
greatly expanded that its transverse measurement is quite three 
times that of the middle of the bone. The tibia has had a large 
cartilaginous pad on its lower end, so that instead of its showing 
an articular surface for the astragalus it presents an almost smooth 
surface to which the cartilaginous pad has been attached. This 
peculiarity has not been hitherto met with in any of the allied 
South African forms, and so far as I am aware only occurs in 
aquatic forms. Among Reptiles a somewhat similar condition is 
seen in the Pythonomorpha and in Plesiosaurians. 
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