hatcher: diplodocus (marsh) 15 



pophyses and neural spines in their relations to each other have a certain resem- 

 blance to that of the yard-arms and masts of a ship. In the seven posterior dorsals 

 the diapophyses are situated high above the centra, all approximately in the same 

 plane. Commencing Avith the fourth dorsal and continuing anteriorly the dia- 

 pophyses gradually become shorter and assume a less elevated position, until in the 

 first dorsal the position is about on a level with the superior border of the centrum. 

 This relative position is maintained throughout the cervical series. There are promi- 

 nent rugosities developed near the extremities of the diapophyses. These are smaller 

 and look upward in the posterior dorsals, but larger, and with their surfaces directed 

 outward in the anterior dorsals. They doubtless served for muscular attachment. 



The Zyg apophyses. — The caudals and posterior dorsal vertebrse articulate by rather 

 small and in the latter series much elevated zygapophyses. In the posterior dorsals 

 the articular surfaces are small and continued into those characteristic compound 

 articulations designated by Marsh as the dlplospheiial and by Cope as the hyposphenal 

 or hyposphene-hypantrum articulations. 



In the anterior dorsals and in the cervicals the zygapophyses are lower, more ex- 

 panded transversely, with greatly enlarged articular surfaces, which describe more or 

 less accurately the arc of a circle, the anterior looking upward and inward and the 

 posterior downward and outward. 



Rih Facets. — Each dorsal vertebra in Diplodocus bears a rib, and in all but the 

 last dorsal these ribs are movable and articulate with their respective vertebrae by 

 two facets, a tubercular facet placed on the extremities of the diapophyses and a 

 capitular facet situated anterior and inferior to the tubercular facet and placed either 

 on the side of the neural arch, or of the centrum. The tubercular facets in dorsals 

 five to ten inclusive occupy the extremities of the diapophyses. They look directly 

 outward and during the life of the individual, when in its normal quadrupedal po- 

 sition, these facets, together with the zygapophyses of these vertebrae, lay in approx- 

 imately the same plane, which was inclined slightly forward. Commencing with 

 the fourth dorsal and in the preceding anterior dorsals the diapophyses rapidly as- 

 sume a position inferior to that of the zygapophyses of their respective vertebrge, 

 and their extremities are deflected so that in the third and fourth dorsals the tuber- 

 cular facets look downward and outward. In dorsals one and two this deflection 

 becomes very pronounced, is continued as an inferior extension of the diapophyses, 

 and the tubercular facets look directly downward, so that in dorsal one they are on 

 a line with the middle of the centrum. 



Commencing with dorsal six and continuing- throughout the succeeding dorsals 

 the capitular facets all occupy the same plane, which is slightly inferior to that of 



