DHTOSAURIA. 131 



Order D1NOSAURIA. 



Body and limbs varying from a more or less lacertiform to an 

 ornithoid type, the latter feature being especially shown in the 

 pelvic girdle and limb ; pelvic limbs moderately or very long ; body 

 with or without dermal armour, which does not take the form of 

 pitted imbricating scutes. Vertebrae very generally amphiccelous, 

 but frequently opisthoccelous in the cervico-dorsal, and very rarely 

 proccelous in the caudal region ; neuro- central suture persistent till 

 a late date ; usually from three to six sacral vertebrae, but occasionally 

 only two ; cervical ribs without long antero-posterior processes ; no 

 uncinate processes to ribs ; rib-facets of middle dorsal vertebrae 

 sometimes forming a " step " on the transverse process, and in other 

 cases placed on the lamina of the arch. Skull relatively small ; 

 palate imperfectly known, but probably in some cases approaching 

 the type of the Parasuchian Crocodilia, and in others of the Rhyn- 

 chocephalia ; quadrate not wedged in among adjacent bones ; mandi- 

 bular symphysis cartilaginous ; a columella and sclerotic ossifications 

 in some instances. Teeth with compressed and often complex 

 crowns ; not always implanted in distinct sockets. Sternal region 

 not fully known, but frequently a pair of symmetrical ossifications, of 

 which the exact homology is in some cases doubtful, and apparently 

 no clavicles 1 . Limb-bones solid or hollow ; coracoid short, with 

 fontanelle; humerus with head more differentiated than in the 

 Crocodilia, and the deltoid crest terminating less abruptly. Ilium 

 (fig. 21) with distinct pubic and preacetabular processes; pubis 

 (fig. 21) entering into acetabulum, directed backwards or forwards ; 

 ischium frequently with obturator process, and slender. Femur with 

 curved or straight shaft, head either oblique or at right angles to 

 condyles, and with or without inner trochanter ; tibia with cnemial 

 crest; astragalus frequently flattened and applied to tibia. Habits 

 quadrupedal or bipedal. 



The less specialized forms approximate to the generalized Croco- 

 dilia and it is probable that in the Lower Trias the two orders were 

 indistinguishable ; there are also indications of affinity with the 

 Ehynchocephalia. 



Suborder SAUROPODA. 

 Premaxilla completely toothed ; nares (fig. 19), when known, in 

 middle of skull ; a large preorbital vacuity ; quadrate with condyle 



1 The so-called clavicles of Iguanodon are noticed below, where they are 

 provisionally referred to the sternal region. 



k2 



