1 1 52 CLASS REPTILIA. 



was sometimes defended by a bony dermal armour, which may 

 carry long spines, but apparently was never composed of imbricating 

 pitted scutes. The centra of the vertebrae are very generally amphi- 

 ccelous ; but are not unfrequently opisthoccelous in the cervical, and 

 more rarely in the anterior dorsal region ; and occasionally some of 

 the caudals are proccelous. The neuro-central suture was usually 

 persistent till an advanced period of life. As a general rule the 

 sacrum includes from three to six vertebrae, but occasionally the 

 number is reduced to two. The cervical ribs are not produced into 

 spines directed antero-posteriorly • and there are no uncinate pro- 

 cesses to the ribs. The rib-facets of the middle dorsal vertebrae 

 may either form a " step " on the transverse process, as in the Cro- 

 codilia, or may be placed on the lamina of the arch. The skull has 

 many features of that of the earlier Crocodilia, but also seems to 

 approximate in some cases to the Rhynchocephalian type. The pre- 

 maxillae were but rarely fused together ; and the union of the man- 

 dibular rami in the symphysis is cartilaginous. The teeth are gen- 

 erally more or less laterally compressed, frequently having serrated 

 edges, and may be of complex structure ; they were not always 

 implanted in distinct sockets. The sternal region is imperfectly 

 known, but it frequently comprised two paired bones, which may 

 represent parts of the sternum. The limb bones may be either 

 solid or furnished with a medullary cavity. The coracoid has a 

 fontanelle, and is always short and rounded. In the pelvis (fig. 

 1060) the ilium has both the pubic and preacetabular processes 

 well developed, the latter being in some cases greatly elongated ; 

 the pubis always takes a share in the formation of the acetabulum 

 (of which the inner wall is unossified), and may be directed either 

 forwards or backwards. The femur may have its head placed either 

 obliquely (as in the Crocodilia) or at right angles to the condyles ; 

 and may or may not be furnished with an inner trochanter. The 

 tibia, as in Birds, had a cnemial crest ; and the astragalus was fre- 

 quently flattened, and more or less closely applied to the lower end 

 of the tibia. 



Suborder i. Ornithopoda. — This suborder is taken to include 

 the Stegosauria of Professor Marsh, and embraces the most special- 

 ised forms. In the skull (figs. 1059, 1062) the anterior part of the 

 premaxilla is devoid of teeth ; there is no preorbital vacuity ; the 

 nares are placed at the extremity of the skull ; and the teeth are 

 more or less complex, and are frequently not set in distinct sockets. 

 The vertebrae are solid throughout. The pectoral limb is consider- 

 ably shorter than the pelvic ; the limb bones may be either solid 

 or hollow. The ilium generally has its preacetabular process much 

 elongated (fig. 1060), although this is not the case in the type of 

 Camptosaurus (fig. 1052), the ischium has an obturator process; 



