ON ANIMALS BETWEEN BIKDS AND EEPTILES. 
243 
The Dinosauria, a group of extinct reptiles, containing the 
genera Iguanodon, Hadrosaurus, Megalosaurus, Poihilo- 
jpleuron, Scelidosaurus, Plateosaurus,&c.,yvhich. occur through- 
out the whole series of the Mesozoic rocks, and are, for the most 
part, of gigantic size, appear to me to furnish the required 
conditions. In none of these animals is the skull,* or the cervical 
region of the vertebral column, completely known, while the 
sternum and the manus have not yet been obtained in any of 
the genera. In none has any trace of a clavicle been observed. 
With regard to the characters which have been positively deter- 
mined, it has been ascertained, that: 1. From four to six 
vertebrae enter into the composition of the sacrum, and become 
connected with the iJia in a manner which is partly ornithic, 
partly reptilian. 2. The ilia are prolonged forwards in front of 
the acetabulum as well as behind it, and the resemblance to the 
bird’s ilium thus produced is greatly increased by the widely 
arched form of the acetabular margin of the bone, and the ex- 
tensive perforation of the floor of the acetabulum (Plate XXVIII. 
fig. 3, IL), 3. The other two components of the os innomina- 
tum have not been observed actually in place ; indeed, only 
one of them is known at all, but that one is exceedingly re- 
markable from its strongly ornithic character (Plate XXVIIL 
fig. 3, Is,). It is the bone which has been called clavicle ” in 
Megalosaurus and Iguanodon by Cuvier and his successors, 
though the sagacious Buckland had hinted its real nature.f But 
these bones are not in the least like the clavicles of any animal 
which possesses a clavicle, while they are extremely similar to 
the ischia of such a bird as an ostrich (Plate XXVIII. fig. l./s.) ; 
and in the only instance in which they have been found in toler- 
ably undisturbed relation with other parts of the skeleton, 
namely, in the Maidstone Iguanodon, they lie, one upon each side 
of the body, close to the ilia. I hold it to be certain that these 
bones belong to the pelvis, and not to the shoulder-girdle, and 
I think it most probable that they are ischia ; but I do not deny 
that they may be pubes. 4. The head of the femur is set-on at 
right angles to the shaft of the bone, so that the axis of the 
thigh-bone must have been parallel with the middle vertical 
plane of the body, as in birds. 5. The posterior surface of the 
external condyle of the femur presents a strong crest, which 
passes between the heads of the fibula and the tibia as in birds. 
There is only a rudiment of this structure in other reptiles. 6. 
* The cranium of Scelidosaurus is most completely preserved, but lacks 
the extremity of the snout. 
t The so-called coracoid ” of Megalosaurus is the ilium. I am indebted 
to Professor Phillips, and to the splendid collection of Megalosaurian remains 
which he has formed at Oxford, for most important evidence touching this 
reptile. 
