On Lost Forms between Birds and Reptiles. 363 



3. The other two components of the os innomnatum have not been 

 observed actually in place ; indeed, only one of them is known at 

 all, but that one is exceedingly remarkable from its strongly ornithic 

 character. It is the bone which has been called " clavicle" in Mega- 

 losaurus and Iguanodan by Cuvier and his successors, though the 

 sagacious Buckland had hinted its real nature.^ 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 ; and in the only instance in which they have been 

 found in tolerably 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 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 

 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 pre- 

 sents a strong crest, which passes between the head of the fibula and 

 the tibia as in birds. There is only a rudiment of this structure in 

 other reptiles. 



6. The tibia has a great anterior or " procnemial" crest, convex on 

 the inner, and concave on the outer, side. Nothing comparable to this 

 exists in other reptiles, but a correspondingly developed crest exists 

 in the great majority of birds, especially such as have great walking 

 or swimming powers. 



7. The lower extremity of the fibula is much smaller than the 

 other ; it is, proportionally, a more slender bone than in other reptiles. 

 In birds the distal end of the fibula thins away to a point, and it is a 

 still more slender bone. 



8. Scelidosaurus has four complete toes, but there is a rudiment of 

 a fifth metatarsal. The third or middle toe is the largest, and the 

 metatarsal of the hallux is much smaller at its proximal than at its 

 distal end. 



Iguanodon has three large toes, of which the middle is the longest, 

 The slender proximal end of a first metatarsal has been found adherent 

 to the inner face of the second, so that if the hallux was completely 

 developed it was probably very small. No rudiment of the outer toe 

 has been observed. 



It is clear, from the manner in which the three principal meta- 

 tarsals articulate together, that they were very intimately and firmly 

 united, and that a sufficient base for the support of the body was 

 afforded by the spreading out of the phalangeal regions of the toes. 



From the great difference in size between the fore and hind limbs, 

 Mantell, and more recently Leidy, have concluded that the Dino- 

 sauria (at least, Iguanodon and Hadrosaurus) may have supported them- 



^ The so-called " coracoid" of Megalosaurus is the ilium. I am indehted to Pro- 

 fessor Phillips, and to the splendid collection of Megalosaurian remains which he hag 

 formed at Oxford, for most important evidence touching this reptile. 



