38 PROCEEDINGS OF THE NATIONAL MUSEUM vol. G9 



DORSAL VERTEBRAE 



It is fortunate that this vertebral column (pi. 1, fig. 1) is intact 

 from the atlas to the fifth lumbar. Because of this fact one can state 

 definitely that the dorsal series consists of not more than 10 vertebrae. 

 With the exception of the extremities of the neural spines and the 

 right transverse processes of the ninth and tenth dorsals, all of these 

 vertebrae are practically complete. The epiphyses of some are loose 

 and a f cav are missing entirely. The neural arches of all of the dorsal 

 vertebrae are crushed in one direction or another and this must be 

 taken into consideration whenever the measurements given on page 41 

 are utilized for purposes of comparison. As regards the posterior 

 dorsals, the centra are slenderer and the neural spines relatively 

 wider than those of Delphinodon dividum. As compared to those of 

 Sot alia guianensis,^^ they differ chiefly in the relative lengths of 

 the centra of the corresponding vertebrae and in the proportions of 

 the neural spines. The posterior dorsal vertebrae of this fossil por- 

 poise differ noticeably from the corresponding vertebrae of many 

 living delphinoids in that the neural spines in proportion to the 

 height of the vertebrae are short and wide, instead of being elon- 

 gated. 



The relation between the length and width of the centrum, the 

 shape of the neural spine, the width of the interval between the 

 prezyapophysial facets, as well as the peculiarities of the diapo- 

 physis, including the position of the facet for the tuberculum, will 

 serve as a guide for determining the position of any dorsal in the 

 series. The centra increase in length from the first to the last, the 

 centrum of the tenth dorsal being more than three times as long as 

 the first. The epiphyses of all the dorsals are relatively thin. There 

 is no transitional dorsal with paired facets for articulation with the 

 cori-esponding rib. Slender neural spines with recurved extremities 

 are the chief peculiarities of the first three dorsals ; the neural spines 

 of the remaining dorsals are wider anteroposteriorly and have squarely 

 truncated extremities. There is a progressive decrease in the width 

 of the interval separating the prezygapophysial facets from the an- 

 terior to the posterior dorsal. These facets are nearly horizontal on 

 the first seven dorsals, while those of the last three slope obliquely 

 downward and inward. On the first four dorsals the diapophyses 

 are elongated and the facet for articulation with the tuberculum of 

 the rib is situated anterior to the level of the epiphysis, but on the 

 eighth it is entirely behind the level of the epiphysis. The facets for 

 the tubercula increase in length from the first to the eighth dorsals, 

 but decrease in width. On each side of the centrum of the first to the 

 sixth dorsals, inclusive, below the level of the base of the neural 



" Van Beneden, P. J., and P. Gervals, Ost^ographle des C6tac6s vivants et fossiles, 

 Paris, Atlas, pi. 41, flg. 1. 1880. 



