86 , THE EXTINCT BATRACHIA, REPTILIA 



The ilium extended horizontally forwards, and supporting a number of vertebrae 

 anterior to the two sacrals of other Reptilia. Acetabulum perforate, and partly en- 

 closed peripherally by the ilium and pubis. Pubes elongate, parallel ; ischia longitudinal, 

 in plane of ilium, elongate, with distinct head for pubis. Femur with transverse neck and 

 head, and third trochanter. " Cervical and anterior dorsal vertebra? with par and diapo- 

 physes, for articulation with bifurcate ribs." Neural arches of dorsal vertebra; attached 

 by suture ; of sacrals, shifted over the intervertebral sutures. 



The structures presented by the Dinosauria have presented greater difficulty of expla- 

 nation than any other type of extinct vertebrates.* This has in part resulted from the 

 attempt so assign them to types already known, and to explain their structures in accord- 

 ance therewith ; a course scarcely consistent with our present knowledge of the peculiari- 

 ties of the parts themselves. The type is a good illustration of the necessity of 

 interpreting extinct forms by a combination of the " law of successional relation," with 

 " the law of types " or of morphological " correllation," and not by either alone. 



The direction assigned to pubes in this order, is suggested by considerations explained 

 below. They have probably diverged forwards and downwards from the vertebral column 

 and their great length indicates a prominent abdomen.. The only Dinosaurs where they 

 are preserved in place, the Stenopelix valdensis of Von Meyer, and Compsognathus 

 longipes of Wagner, justify this proposition. The ischium in Stenopelix and Teratosaurus 

 is a broad flattened bone slightly curved in the lateral direction, and of sufficient strength 

 with its fellow, to support the weight of the animal when in a sitting posture. The 

 pubes in Hadrosaurus and Compsognathus are much more slender and proximally dilated ; 

 as in the Crocodiles the chief support of each is derived from the articulation with an 

 anterior tuberosity of the ischium. The articulation with the ischium is probably wanting 

 or very slight and ligamentous, and the acetabulum was thus open, a large foramen being 

 included by the three bones which usually compose it. 



The head of the femur is transverse to the direction of motion of the condyles, and 

 not oblique as in modern lizards. Hence the motion of this element was in a line paral- 

 lel with the axis of the body, and the limb could not be directed obliquely from that axis 

 so as to allow the body to rest on the ground between them in the ordinary progression of 

 the animal, as is the case with Iguanas, Crocodiles, etc. 



The fore limbs appear to have been weak, even when somewhat elongate, as in 

 Iguanodon. Their articulation with the scapula is a singular part of the structure. In 



* For discussions of these relations see Proceed. Ac, Nat. Sci., Phila., 1866, 317, and Proceed. Amev. Philos. 

 Soc, 1869, 16. 



