ORDER DINOSAURIA. II71 



enter upon the consideration of the largest known Dinosaurs, and 

 those which make so many marked approximations to the more 

 generalised Crocodilia as to show how close is the relationship 

 between that order and the Dinosauria. 1 The skull (fig. 1076) 

 agrees with that of the Theropoda in having the premaxillse com- 

 pletely toothed, and also in the presence of a large preorbital 

 vacuity ; but the external nares formed long slits in the fore part of 

 the skull as in Ornithosaurs and Birds. The teeth are invariably 

 set in distinct sockets and are of a spatulate form, without marginal 

 serrations (fig. 1072). The sternal bones are ovate. All the ver- 

 tebrae in advance of the sacrum, and sometimes those of that region 

 also, have a large vacuity 

 on each side of the cen- 

 trum communicating with 

 a series of internal cavities, 

 which give a honeycomb- 

 like Structure tO the Whole Fig. 1072.— Outer side of a tooth of Morosaurus 

 „ , i (-pi ■ „ «• j grandis ,* from the Upper Jurassic of North America. 

 Vertebra. ThlS affords a (W half natural size. (After Marsh.) 



combination of strength 



and lightness in the massive supports necessarily required for the 

 huge ribs, limbs, and muscles, which could not have been attained 

 in any other manner. All the anterior vertebrae are opisthoccelous ; 

 and in the cervical region the ribs are anchylosed to the vertebrae, 

 which have no neural spines, and are longer than the dorsals ; while 

 the spines of the latter are laterally expanded ; and in the sacrum 

 each centrum supports its own arch. The limb bones are solid ; 

 and since the pectoral limb is not much shorter than the pelvic, it 

 appears that these Reptiles were habitually quadrupedal. All the 

 feet were plantigrade, and furnished with five digits ; those of the 

 pes being terminated by large curved claws. The ilium (fig. 1073) 

 has its upper border only moderately arched and its postacetabular 

 portion short; while the pubis (fig. 1073), which is directed down- 

 wards and forwards, is stout with a comparatively small distal expan- 

 sion, where it unites by a cartilaginous symphysis with its fellow of 

 the opposite side. The ischium (fig. 1073) is likewise a stout bone 

 agreeing with that of the Crocodilia in the absence of an obturator 

 process ; and the two ischia have a peculiar incurving of their distal 

 extremity where they meet in a symphysis. 



It may be observed that in the lateral views of the pelvis shown in the 

 figures, where the bones are drawn more or less nearly in a vertical 

 plane, it is impossible to give a true idea of the peculiar contour of the 

 distal extremity of the pubis and ischium. These bones are really con- 

 cave from above downwards on the outer (figured) aspect, and convex on 



1 Professor Cope would include the Sauiopodous Dinosaurs in the Crocodilia. 



