l88 PATAGONIAN EXPEDITIONS: PALEONTOLOGY. 



having an almost semicircular free border, making the greatest breadth of 

 the vertebra in the middle of its course and not at the hinder border ; in 

 front the processes extend to the border of the anterior cotyles, from 

 which they are separated by notches in the Pleistocene genus ; the hinder 

 margins do not extend beyond the posterior cotyles, as they conspicuously 

 do in Mylodon. The posterior opening of the vertebrarterial canal has a 

 somewhat more forward position than in the latter, in which the foramen 

 is concealed when the vertebra is seen from above ; the canal divides 

 almost immediately, one branch piercing the neural arch and the other 

 passing forward and downward through the transverse process and open- 

 ing on the ventral side ; in front of this ventral opening is another canal 

 which perforates the transverse process obliquely forward and upward. 

 Among the Pleistocene Gravigrada Megalonyx most resembles the pres- 

 ent species in the course of these canals. 



The axis has a short, wide, depressed centrum, with ventral keel termi- 

 nating in a tubercle on the hinder border, and with transversely oval and 

 very slightly concave posterior face ; the anterior facets for the atlas are 

 relatively larger than in the Pleistocene genera and differ in shape and 

 position, projecting much farther below the centrum and rising less upon 

 the sides of the neural canal. The odontoid process is relatively longer, 

 more slender and pointed than in Mylodon, less so than in Megalonyx, 

 while the neural canal is larger than in any of the Pleistocene genera and 

 the arch wider ; the neural spine is broken away, but was evidently thin. 

 The transverse processes are quite short and slender, more so than those 

 of Megalonyx, which otherwise they resemble ; the vertebrarterial canal is 

 also as in this genus. 



The other cervical vertebrae are much damaged and the sixth and 

 seventh have been lost. The third vertebra is considerably smaller than 

 the axis ; the centrum is depressed and oblique, with transversely oval 

 faces, is slightly opisthoccelous and has a well-defined ventral keel. The 

 pedicles of the neural arch are low, but the arch itself is broad and is 

 flattened on the dorsal side ; the zygapophyses are large, especially the 

 anterior pair. The spine and transverse processes are missing. 



The fourth cervical is like the third, but it is somewhat smaller and has 

 a less prominent keel ; the transverse process is a slender rod, extended 

 in the fore-and-aft direction and perforated at the base. The fifth is 

 slightly smaller than the fourth. 



