Revieics — Dollo's Dinosauria of Bernissart. 125 



extremities of the neural spines. Just as the lifting of this weight 

 from the ground would be a purposeless expenditure of strength 

 when the animal was at rest, so I think the analogy of the Crocodile, 

 which is not quite incomparable in caudal structure, may be appealed 

 to in evidence that the tail was carried in a lower position than 

 M. Dollo gives it. To bring this result about we must flex the 

 limb more at the knee, so as to make the femur more nearly hori- 

 zontal, and incline the tibia further forward, which would give a 

 more easy, and I think more natural position, than the expectant 

 attitude into which the animals are at present hoisted. The bones 

 of the posterior extremity are well described. Evidence is given 

 that the outer distal condyle of the femur articulates with the 

 cnemial crest of the tibia, and that the fibula, which is shorter than 

 the tibia, has its distal extremity brought in front of the tibia, in the 

 way indicated by Marsh in the Archceopteryx, so as to articulate with 

 a proximal facet of the calcaneum, a portion of which is applied to 

 the tibia. The author does not clearly distinguish in his description 

 between the two types referred to Iguanodon ; but since he states that 

 the two bones of the proximal series of the tarsus articulate with each 

 other, the description may well refer to I. Bernissartensis, in which 

 we know, from other evidence, that this condition obtains. The 

 distal tarsal row, not hitherto described in Iguanodon, is said to 

 consist of three bones. A thin bone articulates proximally with the 

 astragalus, and distally with the first and second metatarsals; a 

 second bone, rather stouter, lies between the astragalus and the 

 third metatarsal ; and the third, of intermediate size, rests on 

 the fourth metatarsal, and articulates with the calcaneum. This 

 distal row is noticed as being quite as avian in general character as 

 the proximal I'ow. The author describes the metatarsus, which has 

 long been well known in Iguanodon Mantelli. He points out that 

 the second to fourth metatarsals are the three usually developed in 

 birds, and that the bones are placed with regard to each other as in 

 birds, so that the middle metatarsal is slightly displaced forward 

 distally, and backward proximally. The number of phalanges 

 corresponds with the number in lacertilians and birds, being 3-4-5. 



Finally, M. Dollo adopts the dictum of Huxley that if the 

 structures between the ilium and the digits of a young fowl are 

 supposed to augment to the bulk of a Dinosaur, and then to be 

 ossified and fossilized, there would be no characters to separate the 

 corresponding parts from those of these gigantic reptiles. There 

 is no doubt much truth in this generalization, which we should be 

 disposed to accept in principle so far as Iguanodon is concerned. If it 

 were worth while for M. Dollo to pursue his line of argument concern- 

 ing the avian characteristics of the Dinosaurian pelvis and hind limb, 

 practically to the exclusion of all other resemblances, the comparisons 

 must derive their importance from being steps in a chain of proof, 

 either that Dinosaurs have acquired their avian characteristics in 

 consequence of the muscular development and functions of the 

 posterior extremities being avian, in types like Iguanodon, or else that 

 these genera, in which avian characters culminate, are ancestors of 



