232 REPTILIA class iii 



9 spatulate, with anterior and posterior cutting edges. Cervital and anterior dorsal 

 vertebrae opisthocoelous and much hollowed on each side ; the rest amphiplatyan. 

 Neural canal much expanded in the sacrum. Fubes moderately long, projecting 

 simply downwards, and united distally hy cartilage ; no post-pubic process. Limb 

 bones solid, feinur without prominent inner trochanter. Fore-limbs only slightly 

 shorter than the hinder pair. All fourfeet semiplantigrade, with five more or less 

 reduced digits ; distal row of carpals and tarsals apparently unossified. Dermal 

 armour absent. 



The Sauropoda display closer relationships with Crocodilians than do the 

 other Orders of Dinosaurs, and share a number of features in common with 

 the Parasuchio,. In this order are included some of the most prodigious land 

 animals known. Their dentition and nature of the articulations prove clearly 

 that they were herbivorous, and the parity of their limbs demonstrates the 

 gait to have been in most cases quadrupedal. Dollo has suggested, how- 

 ever, that the latter habit was possibly secondary, and that all these animals 

 were at one stage bipedal like the Iguanodonts, which have a similar form 

 of pelvis. 



The skull is incompletely known except in the genera Diplodocus, Moi'o- 

 saurus, and Brontosaurus. Teeth of long cylindrical or spatulate aspect, and 

 with anterior and posterior cutting edges, are present in the paired premaxillae 

 and in at least the anterior portion of the maxillae. The orbits are large and 

 laterally directed, the antorbital vacuities are also extensive, and the external 

 nares elongated. The position of the latter is between the premaxillae, 

 maxillae, and nasals. A predentary bone is not developed. 



The cervical and anterior dorsal vertebrae are opisthocoelous, and much 

 hollowed along the sides. The double-headed cervical ribs are fused in part 

 at least with their respective centra and neural arches, and the neural spines 

 are reduced or paired, as in Diplodocus. In the posterior dorsal vertebrae 

 there is a hyposphene-hypantrum arrangement, as well as pre- and post- 

 zygapophyses. The centra of the dorsal vertebrae (Fig. 334), and sometimes 

 also of the other regions, contain large interior cavities, which were probably 

 pneumatic during life. These Chambers, of which there are one or more on 

 each side, are separated by a median longitudinal septum, not always con- 

 tinuous, and open outwardly by a foramen or elongated aperture near the 

 base of the neural arch. In the presacral and anterior caudal vertebrae, the 

 neural arches and spines are likewise hollowed. Each sacral vertebra 

 Supports its own rib. In Diplodocus the arches formed by the diapophysial 

 laminae of the sacrum have their origin in the union of two laminae springing 

 from distinct vertebrae, while each pair of sacral ribs originates from a single 

 centrum. The neural canal in the sacrum is expanded to twice or three times 

 the diameter of the brain cavity. The posterior caudals have solid centra, 

 slightly concave behind, and flat or more rarely concave in front. Chevron 

 bones are well developed. 



In the pectoral arch the scapula is elongated, and much more expanded 

 distally than at , its proximal end. The coracoid is small, more or less 

 rounded anteriorly, and suggestive of the corresponding element in Rhyncho- 

 cephalians. The humerus has a distinct head, and is somewhat crocodilian- 

 like. The pelvic bones are never coössified, and the acetabulum is open. 

 The ilium exhibits only a slight pre-acetabular extension, and the slender 

 ischium is without an obturator process. The pubes are stout, directed 



