ORDER DINOSAURIA. 



"53 



but the most striking and remarkable feature in the group, and one 

 in which it differs from all others except Birds, is that the shaft of 

 the pubis is directed backwards more or less nearly parallel with the 

 ischium, while a shorter and thicker portion in advance of the 

 acetabulum projects forwards. How remarkably this pelvic struc- 

 ture approximates to that of Birds may be seen by comparing figs. 

 1052 and 1060 with that of the pelvis of a Ratite Bird given in the 

 sequel. Thus the large preacetabular process of the pubis of the 

 Dinosaur corresponds with the much smaller but similarly situated 



Fig. 1052. — The left side of the pelvis of Cnmptosaurus disftar ; from the Upper Jurassic of 

 North America. One-twelfth natural size. The upper bone is the ilium, that on the left the 

 pubis, and that on the right the ischium. (After Marsh.) 



pectineal process in the pelvis of the Ratite Birds (fig. 1107). In 

 some cases the pubis had no median symphysis. All the more 

 specialised members of the suborder appear to have walked habitu- 

 ally on the hind limbs alone. In this and the following suborder 

 the length of the tibia is often nearly equal to that of the femur ; 

 and in Hysilophodon and Compso- 

 gnathus the former bone, as in 

 Birds, is the longer of the two. 



Family Trachodontid^e. — 

 The most specialised, as well as 

 one of the most recent, families of 

 the suborder, seems to be that typ- 

 ically represented by the genus 



Trachodon (Hadrosaurus). This family, although closely related 

 to the next, is distinguished by having the teeth arranged in a 

 number of vertical columns and articulating together so as to 



Fig. 1053.— Tooth of Trachodon Foulki , 

 from the Upper Cretaceous of New Jersey. 

 (After Leidy.) 



