12 memoirs op the carnegie museum 



General Characters of the Vertebral Column. 



The Sauropoda have been considered as the least speciahzed of the Dinosauria, 

 and in many respects this is doubtless true, but in its adaptation for the application 

 of those mechanical principles which combine maximum strength with minimum 

 weight and increased surface for muscular attachment, the vertebral column of Dip- 

 lodocus exhibits a remarkable degree of specialization, unsurpassed if not unequaled 

 by other vertebrates. 



The centra throughout the entire series are invaded on either side by large 

 lateral cavities {jjleurocenfral cavities), while the interior instead of consisting of solid 

 bone is made up of numerous cavities enclosed by an intricate series of thin bony 

 plates. These meet and cross at every conceivable angle and abut against the thin 

 outer walls of the centra in such manner as to afford the greatest possible resistance 

 to external strains. 



The neural arches, neural spines, transverse processes, and zygapophyses are either 

 constructed of or supported by laminse, which come in contact with the respective 

 parts in such manner as to give the greatest possible support with the least possible 

 weight. The position and direction of these laminse are so arranged in each ver- 

 tebra as to afford the greatest resistance in the direction of the greatest strains and 

 stresses which were brought to bear upon the various parts in the necessary move- 

 ments during the life of the individual. By reason of this the position and direc- 

 tion of these laminse are quite dissimilar in different parts of the vertebral column. 

 Not only is any single vertebra unlike the preceding or succeeding one, but so vari- 

 able are the positions of the several laminas, buttresses, etc., that they frequently 

 occupy quite different positions, on opposite sides of the same vertebra, sometimes 

 resulting in a remarkable asymmetry. This asymmetry and the dissimilarity noticed 

 in adjacent vertebrae of Diplodocus render it necessary to give a detailed description 

 of each of the presacrals even at the risk of being tedious. 



Before proceeding with the detailed description of the several vertebras, it may 

 be well to give a general description of the vertebral column as a whole. 



By a glance at the accompanying restoration it will be seen that the sacrum is 

 the central or nodal point in the vertebral column. Not only are the presacral and 

 caudal regions subequal in length, but the individual vertebr£e of the former are 

 opisthocoelous, while those of the latter are procoelous. Moreover the long, co- 

 ossified sacral spines are replaced anteriorly and posteriorly by the free simple spines 

 of the adjacent dorsals and caudals, which, as we recede from the sacrum, rapidly 

 become shorter and emarginate at the apex, resulting anteriorly in a pair of trans- 

 versely placed neural spines widely separated above but converging below. These 



