1869. ] HUXLEY—DINOSAURIA AND BIRDS. 29 
tibia, fibula, and astragalus of such a typical Dinosaurian as Megalo- 
saurus, let us compare these bones with the corresponding bones of 
Reptiles and Birds, as we have compared the pelvis. 
In Reptiles (ordinary Lacertilia and Crocodilia, namely, which 
are alone at present under consideration) ,— 
1. The proximal end of the tibia has but a very small or quite 
rudimentary cnemial crest, and it presents no ridge for the fibula on 
its outer side. 
2. The flattened sides of the distal end of the tibia look, the one 
directly forwards, or forwards and inwards; and the other back- 
wards, or backwards and outwards. And when the posterior edges 
of the two condyles of the proximal ends of the tibia rest on a flat 
surface which looks forwards, the long axis of the distal end is 
either nearly parallel with that surface, or is inclined obliquely 
from in front and without backwards and inwards. 
3. There is no depression in the anterior face of the tibia for the 
reception of an ascending process of the astragalus. 
4, The distal end of the fibula is as large as, or larger than, the 
proximal end, and articulates largely with a facet on the outer 
part of the astragalus. 
5. The astragalus is not depressed and flattened from above 
downwards, nor does it send a process upwards in front of the tibia. 
6. The astragalus remains quite free from the tibia. 
In all these respects any ordinary bird, say a fowl, is very 
strikingly contrasted with the reptile. 
1. The proximal end of the tibia is produced forwards and out- 
wards into an enormous cnemial crest; and, on the outer side, 
there is a strong ridge for the fibula. 
2. When the posterior edges of the condyles of the tibia rest upon 
a flat surface, the one flat surface of the distal end of the bone 
looks outwards as well as forwards, and the other inwards as well 
as backwards, and the axis of the distal end is inclined at an angle 
of 45° to the flat surface from within and in front, backwards and 
outwards, thus exactly reversing the direction in the Reptile. 
3. There is a deep longitudinal depression on the anterior face of 
the distal end of the tibia, which recelves an ascending process of 
the astragalus. 
4. The distal end of the fibula is a mere style, and does not di- 
rectly articulate with the astragalus. 
5. The astragalus is a much-depressed bone, with a concave prox- 
imal and a convex, pulley-like distal surface. A process ascends 
from its front margin in the groove in the front face of the tibia. 
This process is comparatively short, and perforated by two canals 
for the tibialis anticus and ewtensor communis in the Fowl, while in 
the Ostrich and Emu it is extremely long and not so perforated. 
6. The astragalus becomes ankylosed with the tibia (though it re- 
mains distinct for a long time in the Ostrich and Rhea, and in some 
breeds of fowls). 
Now in every one of these particulars, except perhaps the last, 
Megalosaurus is far more like a bird than it is like a reptile. 
