97 



lerior, being known as sucli by its larger (iiapophyscs and much smaller artic- 

 ular surfaces for chevron-bones; it appears probable, indeed, that this one has 

 been without these appendages. It is, therefore, from no great distance 

 behind the sacrum. Its position being thus determined, it may be described 

 in detail as follows : 



As observed, the centrum is elongate and depressed. Tiie inferior sur- 

 face at the cup is flat ; it is then arched upward, descending again to the rim 

 of the ball. The posterior two-thirds has a median groove, which terminates in 

 a deep notch of the ball, which involves one-third of its vertical diameter, and 

 widens backward. The ball is transverse oval, and only moderately convex ; 

 near its upper margin, a small deep pit interrupts its surface, having the 

 appearance of an unusually large ligamentous insertion ; its border slightly 

 excavates the margin of the ball. The cup is a transverse oval, wider below. 

 Its inferior and superior margins are so deeply (but openly) emarginate as to 

 reduce the concavity in the vertical direction very much. From tlie superior 

 emargination, a deep groove descends to below the middle, probably for liga- 

 mentous insertion. The neural canal is subtrilateral. The neural arch is, as 

 usual in this group, deeply emarginate in front, and much prolonged behind. 

 The zygapophyses project beyond the ball, and the arch is contracted in front 

 of them. Its upper surface has neither process nor keel, but is rugose for 

 ligamentous and muscular insertion. The diapophyses have a wide base, and 

 are subcylindric. 



The surface is delicately reticulate rugose; coarsely rugose on the exter- 

 nal faces of the zygapophyses. There are several small nutritious foramina, 

 the largest being in the bottom of the groove of I he lower face. 



Another vertebra differs in being rather more slender, and in having an 

 obtuse keel of the neural arch. The pit of the ball is wanting, and the iiifc- 

 rior emargination. The chevron-articulations are larger; and the groove of 

 the cup occupies its middle, instead of its upper half 



Measurements. 



ii. 



Length of tlio ccntrnm (greatest) 0.027 



Diameter of the cup, vertical 0.01 



Diameter of the cup, horizontal 0. 017 



Elevation of the top of the neural arch above the floor of the noaral canal 0. Oi;5 



L"ngth of tbe arch on the median line above 0. 02 



Width of the arch in front of the posterior zyg.apophysos 0. 012 



A metacarpal or metatarsal bone was found near, though not willi, the 

 vertebra;, and probably belongs to the same animal. If metatarsal, it is much 



