22 PATAGONIAN EXPEDITIONS : PAL/EONTOLOGY. 



ascending ramus, with a broad and deep groove leading back from it 

 toward the condyle, which groove is not shown in Tatu. 



Vertebral Column ; Ribs and Sternum. The cervical vertebrae are of 

 distinctively armadillo-like character and, in particular, resemble those of 

 Tatu. In proportion to the size of the head the neck is short, though 

 decidedly longer than in Dasypus, stout and heavy. The atlas is shaped 

 much like that of Tatu, being short, broad and high and considerably 

 surpassing that of the latter genus in the dorso-ventral diameter. The 

 anterior cotyles are quite narrow and nearly plane transversely, high and 

 concave dorso-ventrally ; each is notched near the ventral side and the 

 articular surface is invaded by a sulcus corresponding to that on the occi- 

 pital condyle. The posterior cotyles are broad, low and quite concave and 

 present obliquely inward. The sides of the atlas are high, flattened, and 

 nearly vertical on their outer faces, meeting the neural and inferior arches 

 almost at right angles, which gives to the bone a characteristically quad- 

 rate shape. The neural arch is narrow antero-posteriorly, the cotyles 

 projecting freely in front of and behind it, and is moderately convex on 

 the dorsal side, while the neural spine is a low, but heavy, rugose and 

 quite conspicuous tubercle. The inferior arch is slender and less strongly 

 curved than the neural. The neural canal is somewhat different in shape 

 from that of Tatu, being considerably higher than it is wide and divided 

 into nearly equal dorsal and ventral portions by the tubercles for the 

 attachment of the transverse ligament, while in the modern genus the 

 lower portion is the larger of the two. As in the existing genus, the 

 transverse process is greatly reduced, though it is more prominent than in 

 the latter, forming merely a roughened and thickened, imperforate eleva- 

 tion on the posterior part of the dorso-lateral angle. The hinder opening 

 of the vertebrarterial canal is above the inner part of the posterior cotyle 

 and is so covered by the extension of the neural arch as to be concealed, 

 except when the atlas is viewed from behind ; the canal passes forward 

 and downward, opening in a conspicuous foramen on the outer side of 

 the bone. The only other foramina are those perforating the neural arch 

 for the passage of the first pair of spinal nerves. 



The axis and the two succeeding vertebrae (Plate IV, fig. i) are com- 

 pletely fused into one long compound bone, though the elements of this 

 may still be distinguished by the sutural lines. In length, the axis makes 

 up nearly one half of the compound mass, exclusive of the odontoid pro- 



