OSTEOLOGY OF RHAMPHOCOTTUS 473 



7. Vertebral column 



Vertebral formula: 12 abdominal + 14 caudal + hypural = 

 27. 



The spine of the atlas is low and the centrum is very short. 

 The zygapophj^ses, however, are strongly developed, as also are 

 the articular facets of the exoccipitals. The ribs are attached 

 to sHghtly elevated tubercles high up on the neural processes. 

 On the succeeding vertebrae the rib attachments descend rapidly, 

 and rudimentary transverse processes appear on the fifth. Oppo- 

 site processes are rather widely separated and are directed ventro- 

 laterally. The transverse processes of the sixth, seventh, and 

 eighth become gradually longer and do not diverge so widely 

 from the median line. The ribs are attached to the distal ends 

 of these processes. No epipleurals are present anterior to the 

 ninth vertebra (fig. 14). 



In the remaining abdominal vertebrae the transverse processes 

 unite ventrally to form rather blunt processes which, in the caudal 

 vertebrae, become produced as the haemal spines. The ribs 

 are attached at the lower extremities of these processes and up 

 about one-third of their length are rather prominent elevations 

 to which the large epipleurals articulate. The last three ab- 

 dominal vertebrae, with their ribs and epipleurals, constitute a 

 characteristic feature of the vertebral column. Figures 15 to 18 

 illustrate these characters. 



The neural spines are strongly developed and are directed 

 somewhat caudally. They increase rapidly in length from the 

 atlas to the fourth vertebra, and then become gradually shorter 

 posteriorly. 



The caudal vertebrae (figs. 19 and 20) present no unusual 

 features. The first five or six haemal spines are long and the 

 first three bear intermuscular bones. All are curved in a de- 

 cidedly caudal direction. The spines are given off from the 

 anterior part of the haemal processes, the latter continuing as 

 delicate lateral walls to the posterior ends of the centra. The 

 last two caudal vertebrae have very strongly developed neural 

 and haemal spines which assist in the support of the hypural. 

 The last three or four vertebrae bear delicate lateral ridges. 



