88 



AMPHIBIA AND PISCES OF THE PERMIAN OF NORTH AMERICA 



vertebrae, and is regarded as the possible attachment of a cartilaginous 

 neural spine. The anterior and posterior zygapophyses and the zygosphene 

 and zygantrum are well developed. There is a low keel on the lower surface 

 which is somewhat broadened at the anterior and posterior ends. On the 

 sides are two well-developed processes for the double-headed ribs; the lower 

 is attached to the centrum and the upper to the neural arch. 



From this point the dorsal vertebrae are quite similar. The centrum 

 is elongate with the lower surface concave antero-posteriorly, and in the 



large specimens nearly flat from side to 

 side near the middle. In smaller speci- 

 mens the lower surface is convex from 

 side to side. There is no trace of a keel 

 on the centrum after the second ver- 

 tebra. The neural spine is heavy and 

 low, with a deep pit, possibly for the 

 attachment of a cartilaginous spine. In 

 the American Museum specimen. No. 

 4472, the processes for the ribs remain 

 distinct to the twelfth or thirteenth, 

 where they fuse and form a strong transverse process, which is quite elongate, 

 with a broad distal end. The last trace of this lateral process disappears on 

 the eighteenth. 



The vertebrae immediately posterior to the second either do not have 

 the pit or it is very much reduced. One, possibly the third, has the spine 

 elevated and rather rugose. The neural arch is very wide, and extends out 

 directly into the transverse process, which bifurcates into upper and lower 

 parts for the rib. The next vertebra following has the spine lower, and there 

 is a deep pit, narrow anteroposteriorly but extending across the spine; the 

 bottom and sides of the pit are smooth. The spine extends much farther 

 posteriorly than the centrum; the posterior end is wider and incloses the 

 anterior end of the following vertebrae. The articular faces of the zyga- 

 pophyses of all the dorsal vertebrae are nearly horizontal. The zygosphene 

 and zygantrum continue through the series. In the majority of the vertebrae 

 the elongate diapophysis and parapophysis rise independently, the former 

 from the arch and the latter from the mid line of the centrum. 



Fig. 21. — D magnicornis. After Broili. XH- 

 Atlas and axis. A, from above; B, from side; 

 C, anterior view of atlas. 



Fig. 22. — D. magnicornis. No. 4472 Am. Mus. X f^. 



A. Sixteenth to nineteenth dorsal vertebra: from below. 



B. Lateral view of second vertebra shown in A. 



The seventeenth vertebra is markedly different from those preceding. 

 The neural spine is lower, and has not the deep pit or notch as in the anterior 

 dorsals. The lower face of the centrum is nearly flat, but is excavated by 

 a deep and wide pit. The posterior edge of this vertebra is thickened and 

 rugose, and articulates by an interlocking suture with the succeeding ver- 

 tebra. This is probably the point of attachment of the posterior limbs and 

 is the degenerate sacrum. 



