MORPHOLOGICAL REVISION 77 



a considerable quantity of cartilage present in the joint. The centrum is more 

 oval in section than in those anterior to the sixth. The spines of the vertebrae from 

 the sixth to the twelfth are exceptionally low and stout, with the distal ends very 

 rugose, either with a median notch or the top expanding like a mushroom, evi- 

 dently to afford attachment to strong ligaments or perhaps to overlying dermal plates. 



With the thirteenth the vertebrae are broader and have less anteroposterior 

 extension of the neural arches and zygapophyses. At the same time the neural arch 

 and spines become higher, so that the whole posterior dorsal series looks thinner 

 and more elevated than the anterior. The articular faces of the transverse processes 

 here begin to shorten and on the fifteenth and sixteenth they reach forward to top of 

 centrum; the lower end no longer passes gently into side of centrum, but stands out 

 abruptly from it. This continues to the twentieth, and on the twenty-first, the first 

 presacral, the transverse process is suddenly shortened and fused with a very short rib. 



There are two sacrals. The spines are abruptly bent backward, leaving a 

 considerable space between the first sacral and the straight spine of the first presacral. 

 The anterior zygapophyses of the first sacral are full-sized, but the articulation 

 between the two sacrals is so close that the zygapophyses have practically disap- 

 peared. The rib is very stout and strong and the distal end is widely expanded and 

 applied to the inner surface of the ilium. The rib of the second is smaller, the distal 

 end less expanded, and it appears to be, in part at least, applied to the expanded 

 surface of the first rib. The intercentrum between the two is fused with the centra. 



The first caudal has the spine sharply curved backward, resembling in this 

 respect the sacrals. The ribs are stout and fused with the transverse processes. The 

 anterior zygapophyses are small, but larger than those between the sacrals. The 

 hyposphene and hypantrum are small but distinct. 



In the second caudal the spine is still recurved and the zygapophyses are large 

 and well formed, but there is no trace of the hyposphene and hypantrum. The 

 ribs are elongate and sharply bent to the rear. 



The third to fifth caudals diminish regularly in size; the spines are straight and 

 the zygapophyses are proportionately larger than in the first two. The transverse 

 processes are large, increasing the width of the vertebrae. The ribs of the fourth 

 and fifth are reduced in length. The first chevron appears between the fourth and 

 fifth, or the fifth and sixth, and continues to the extremity of the tail. 



The sixth to ninth. The transverse processes are much shorter and with the 

 rudimentary ribs stand straight out from the side of the centrum. The centrum is 

 shorter, so that these vertebrae look wider than those before or behind. 



On the tenth is the last trace of a rib; behind this there are only rudiments 

 which rapidly disappear. The vertebrae from the tenth to the twenty-fifth are 

 similar to the tenth; retaining the high spines as they diminish in size, they are more 

 slender in appearance. 



Twenty-sixth to thirty-third. There are thirty-three vertebrae in the tail as 

 mounted; ten of these are plaster models, necessary to complete the sequence, and 

 there were probably a few, four or five, missing at the tip of the tail. Shortly 

 after the twenty-fifth the vertebrae lose their spines and assume an elongate form, 

 though they never approach the proportion seen in forms with elongate, taper tails. 



The chevrons are exceptionally large and lie fairly close to the centra. The 

 upper end is perforated by an elongate foramen which is not complete above, in the 

 anterior part of the tail, but in the middle and posterior part of the tail is closed. 



The ribs. Imperfect remains suggest that the ribs of the atlas and axis were 

 fairly long and slender. That of the third was an elongate plate of triangular form 

 with the anterior edge straight and an angle to the rear overlapping the rib of the 



