1869. ] HUXLEY—DINOSAURIA AND BIRDS. 19 
this bone, the extant descriptions being very imperfect, and some- 
times based upon bones which have been broken and put together 
the wrong way by the mender. In the British-Museum collection 
the only thoroughly trustworthy Jguanodon tibia I can find is the 
small one numbered 36,403. It has been broken into several 
pieces; but they are very well fitted together, and the bone is not 
at all distorted. A second tibia of Jguanodon, with a very good 
proximal end, is numbered 28,669. The distal end of the Megalo- 
saurian tibia (No. 31,809), which has been figured, is imperfect ; but 
there was a tibia of Megalosawrus in the collection, the distal end of 
which was still inserted in its matrix; and, at my request, it was 
very carefully worked out. This tibia is the most perfect I have 
seen. 
Its proximal end is produced into a great cnemial crest, which is 
concave on its outer, convex on its inner side. But when the backs 
of the condyles rest upon a plane surface, the outer edge of the crest 
does not project beyond the outer side of the bone. The inner and 
outer condyles of the proximal end are not very unequal, though 
the outer is the smaller. On the outer side of the proximal end of 
the bone there is a strong longitudinal ridge for the attachment of 
the fibula. The shaft of the bone is somewhat flattened from before 
backwards, and the distal end is still more flattened and expanded. 
Moreover the direction of its faces is quite different from that of 
the principal faces of the proximal end of the bone. These look 
inwards and outwards, supposing the condyle to rest upon a 
posterior plane surface. But the faces of the distal moiety of the 
tibia look forwards and outwards, and backwards and inwards, the 
plane of the distal end of the bone being nearly at right angles to 
that of the proximal end. The antero-external face of the distal end 
presented a somewhat smooth surface, apparently for the articulation 
of a bone; and this surface was bounded above and internally by a 
sharply defined edge, which terminated the face of the shaft of the 
bone. This edge at first passed outwards and backwards, and was 
convex downwards; but having reached the middle of the surface 
of the bone, it turns upwards and is lost at about 1 the length of the 
tibia from its distal end. The distal articular surface is wider in- 
ternally than externally, and its external moiety projects further 
than the internal, so that its inferior contour is oblique and slightly 
sinuated. 
The tibia of Zguanodon is similar in its general characters to that 
of Megalosaurus ; but the two condyles at the proximal end are 
more unequal, and the great cnemial crest is bent over in such a 
manner as to project far beyond the outer side of the tibia when 
the posterior edges of the condyles rest upon a plane surface. There 
is a small facet just beneath the outer condyle, for the proximal 
end of the fibula; but no crest for that bone is developed from the 
outer face of the tibia. The distal half is not so flattened as in Mega- 
loswurus, but more trihedral. Its plane is twisted in the same way in 
relation to the antero-posterior plane of the bone, as in Megalosaurus. 
The distal extremity is divided into a larger antero-internal, and 
c2 
