48 



THE HISTORY OF THE PELYCOSAURIA, WITH 



canal becomes very small in the middle portion. The descending flange at the lower 

 edge of the articular face has become much deeper than in the cervicals. The distal end 

 of the transverse process has disappeared, but the base shows that it stood well out from 

 the body of the neural arch. The slender process from the tubercular to the capitular 

 face is still present, but incomplete at the proximal end, it still bears a small facet. The 

 pit between the base of the transverse process and the base of the spine has become very 

 long and deep, its anterior end is closed as abruptly as the posterior by the rising of the 

 connection between the anterior end of the base of the transverse process and the pru>- 

 zygapophysis. The excavation below the transverse process is partly filled by a 

 swelling out of the base of the; neural spine and is contracted into a, pit at a, point pos- 

 terior to the base of the neural spine. At the base of the pnezygapophysis, the anterior 

 edge of the centrum supports two small processes, one on each side of the neural canal. 

 These correspond to similar processes on the posterior edge of the preceding centrum. 

 The spine is nearly complete, its shape is the same as described in the cervical region, a, 

 plan which persists throughout the whole series of vertebrae. The spine is .<H72 m. long. 

 or a little over twenty-five times the greatest diameter of the centrum. 



The second dorsal differs from the first in a, slight intensification of the char- 

 acters. 



The third and. fourth dorsals are incomplete and injured by decay. A concavity of 

 the sides of the centrum below the level of the chordal canal renders the keel quite thin 

 and prominent. 



The fifth dorsal shows a complete transverse process on the right side. The base 

 presents a pinched appearance due to the presence of two deep pits, one above and the 

 other below the base of the process. The anterior edge of the process has become broad 

 and is marked by a deep groove. The tubercular face looks backwards and downwards, it 

 is broad above and sharp below ; from this sharp, lower, edge a narrow face runs down 

 and inwards for a short distance, it is the remnant of the face connecting the tubercular 

 and the capitular faces in the cervicals. The anterior and the posterior faces of the 

 centrum are inclined slightly toward each other below and the vertical profile is slightly 

 sigmoid, convex opposite the opening of the chordal canal and concave below it. 'Phis 

 leaves quite a space between the lower edges of the opposing vertebra to accommodate 

 the intercentrum. The flanges descending from the lower edges of the articular faces 

 have become quite broad vertically and the excavation of the lower half of the centrum 

 is deepened so that the keel is thin and prominent. The edge of the keel is concave. 

 The spine is incomplete, but even in its imperfect state over twenty-one times the o-reat- 

 est diameter of the centrum. 



The sixth dorsal (PI. II, Figs. 23, 24) shows a very slender base for the transverse 



