THE UPPER TRIASSIC OF WESTERN TEXAS. 39 



ward from the anterior upper angle of the centrum and ends on the anterior face of the 

 posterior ridge as it turns outward on the lower surface of the transverse process, the 

 neural spine is elongate antero-posteriorly. The expanded upper end is wedge-shaped, 

 with the faces of the wedge directed laterally; the spaces between the faces of the wedge 

 are roughened. The lower part of the anterior face of the spine is rendered deeply 

 concave by the development of ridges on each side, which continue downward and 

 outward to end upon the surface of the anterior zygapophyses. The space between 

 these ridges and the zygapophyses is floored by a thin plate of bone which covers the 

 neural canal. On the posterior face of the spine there is a similar development, but the 

 excavation of the face of the spine is much deeper. The faces of the centrum are still 

 transversely oval and the lower surface flat, but the faces are approaching a circular 

 form and the lower surface is becoming rounder. 



The eleventh vertebra has the transverse processes broken away, but the bases 

 are still preserved. The capitular face is now elongate vertically, and a strong ridge 

 runs from its upper origin, above the level of the base of the neural canal, backward 

 and upward to join the posterior ridge which forms the lower arm of the T-shaped 

 transverse process. 



The neural spine is elongate antero-posteriorly and thin transversely. The upper 

 end has a triangular expansion on each side, but the ridges on the edges of the anterior 

 and posterior faces run to the apex. The depression between these ridges is similar to 

 that in the preceding vertebrae; the zygapophyses are closer together. In the tenth and 

 eleventh vertebrae is seen for the first time the deep depression in the floor of the neural 

 canal. The anterior face of the centrum is transversely oval and much larger than the 

 posterior face. This is in part due to the development of the capitular process with its 

 vertical extension. 



In the twelfth vertebra the capitular process rises from a point above the lower 

 edge of the centrum, which is now rounded, and is elongated vertically, the face being 

 nearly twice as high as broad. The ridge upon its upper face, noted as beginning in the 

 eleventh vertebra, is now developed as a strong process which rises as a wall and 

 is united with the lower part of the transverse process at about the naiddle of the 

 length of the latter. The ridge from the posterior corner of the centrum is still 

 strong at its origin, but has become obsolete on the transverse process itself; the 

 transverse process is still T-shaped, but the lower flange is now formed by the anterior 

 ridge instead of the posterior one. In this vertebra the transverse plate between the 

 zygapophyses has a different form. From the inner edge of each of the posterior zyga- 

 pophyses a thin plate runs inward to form the transverse plate and there is a vertical 

 extension downward in the form of a very thin septum which reaches to the upper edge 

 of the neural canal, which is not more than half as large as in the cervical vertebrae. 

 There is also a tendency for a similar plate with a vertical septum to form between 

 the anterior zygapophyses. 



In the thirteenth vertebra the transverse process stands out directly from the side 

 of the vertebra and rises slightly in its course, so that the distal end is higher than the 

 origin of the process. The capitular face has now left the centrum entirely and is attached 

 to the transverse process at about its middle portion. This face is supported by three 

 ridges — one very slender, running from the lower edge of the face to the anterior 

 upper angle of the centrum, the second running from the lower edge of the face upward 

 and inward to the lower surface of the base of the anterior zygapophyses; the third 

 ridge is the anterior half of the posterior ridge. Its posterior half, so strong in the 

 preceding vertebrae, is now obsolescent. Its position marks the dividing-line between 

 the capitular and the tubercular portions of the transverse process. This sudden change 

 of position in the capitular face is characteristic of the Crocodilia and the Phytosauria; 



