THE IGUANODON. 



355 



pubis. . . . The post-pubis is long and slender, and directed backward 

 alongside the ischium, as in birds, for a considerable distance beyond 

 the ischial tuberosity. . . . M. Dollo is inclined to follow Professor 

 Marsh in identifying the dinosaurian pubis with the pectineal process 

 of birds, a conclusion which receives most interesting support in the 

 valuable memoir recently published by Miss Alice Johnson, of Cam- 

 bridge, on " The Development of the Pelvic Girdle in the Chick," in 

 which it is shown that in the embryo fowl the cartilaginous represent- 

 ative of the pectineal process is at first much larger and more promi- 

 nent in proportion to the dimensions of the pelvis than subsequently, 

 and becomes gradually reduced as development proceeds. The pecul- 

 iar form of the pelvis is, no doubt, directly connected with the mus- 

 cular arrangements concerned in the erect posture, originated probably 

 in the dinosaurians and transmitted to birds, in which it has been 

 improved upon by the elimination, almost complete, of the original 

 pubis through disuse." 



The fore-limbs are considerably shorter than the hinder ones, and 

 are massive and strong ; and this difference in structure is cited as 

 further though not conclusive evidence of the animal's having main- 

 tained an erect position. As further evidence in the same direction, 

 and of the approach of the type of structure to that of birds, are 

 mentioned the reduction of the volume of the head and thorax as 

 compared with that of reptiles and the position of a large mass of the 

 viscera behind the hip-joint, as in birds, whereby, with the aid of the 

 long tail, the balancing of the head and fore-part of the body was more 

 easily secured. The dorsal spines of the vertebrae are connected with 

 a set of ossified ligaments binding the whole dorso-lumbar region into 

 a rigid mass — another peculiarity in which the structure is strikingly 

 like that of birds. The fore-limbs of the animal have five and the 

 hind-limbs four claws, or toes, leaving a three-toed track. Here, again, 

 is another and probably the most decisive proof that the iguanodon 

 walked on its hind-limbs only. The feet have been compared by M. 

 Dollo with the tridactyl Wealden foot-prints — which the iguanodon 

 only among known Wealden dinosaurians could have made — and have 

 been found to fit accurately. " If the animal had walked on all-fours," 

 Mr. Moseley remarks, "it is impossible but that pentadactyl im- 

 pressions should have occurred with the tridactyl, but such is not the 

 case. Long series of the tridactyl prints are found without a trace of 

 pentadactyl marks. The arrangement of the tridactyl tracks shows 

 that the iguanodon walked on its hind-feet, and did not spring, 

 like a kangaroo, with the aid of its tail. This merely dragged lightly 

 behind, and has left no impression in connection with the foot-tracks." 

 The first finger, or thumb, constitutes a large homy spur, the remains 

 of which when first found were supposed to be the nose-horns of 

 Mantell's ideal. According to M. Dollo's description, the head is rela- 

 tively small, and very much compressed from side to side. The nos- 



