132 



DIX0SAT7RIA. 



more or less in advance of the posterior extremity ; teeth (fig. 20) 

 simple, usually spatulate, and set in distinct sockets ; generally 

 a columella. Vertebrae with zygosphenal articulations ; anterior 

 ones opisthocoelous ; centra of presacrals with lateral vacuities 

 generally communicating with complex internal cavities by which 

 the centra, are more or less penetrated ; cervicals longer than 

 dorsals, with anchylosed ribs and no neural spines ; dorsals with 

 neural spines laterally expanded ; each posterior sacral arch sup- 

 ported by one vertebra ; caudals with or without postzygapophyses ; 



Piff. 19. 



Dvplodocus hwc/ns, Marsh. — Skull ; from the Upper Jurassic of North America. 

 l~. (From the ' Amer. Journ.') 



chevrons double, closed, or open. Rib-facets of dorsal vertebras 

 placed on the arches. Sternal bones ovate. Limb-bones solid, and 

 pectoral limb nearly as long as pelvic ; scapula much expanded 

 proximally, and frequently also distally, with concave anterior border ; 

 coracoid without descending process ; humerus of a Crocodilian 

 type, but with small distinct head, and deltoid crest terminating 

 less abruptly ; five digits in manus and pes, armed with short, 

 thick, compressed claws. Ilium (fig. 21) deep, with short preace- 

 tabular process, and slight arching of superior border ; pubis (fig. 21) 

 directed forwards, with cartilaginous symphysis and small distal 

 expansion ; ischium short and wide, without obturator process ; 

 femur much longer than tibia, with straight shaft, head nearly in 



