HISTORY OF THE EDENTATA 621 



ing vertebrae; usually, the axis and the third to the sixth 

 formed one mass, while the seventh was fused with the dorsals. 

 The joint between the sixth and seventh vertebrae was such as 

 to permit at least a partial downward bending of the head be- 

 neath the carapace, closing its anterior opening with the head- 

 shield. The seventh neck vertebra and all the dorsals, except 

 the last one, were coossified into a heavy ciu-ved rod, the "dorsal 

 tube" ; the conjoined neural arches formedatunnel for the spinal 

 cord and the spines made a continuous ridge. As the hind legs 

 were very much longer than the fore, the back was strongly 

 arched upward from the neck to the hips. The last dorsal, the 

 lumbars and the sacrum were all fused together to form the 

 "lumbo-sacral tube," of which the coossified neural spines made 

 a very prominent ridge, the principal support of the carapace in 

 the median line ; the anterior half of the trunk skeleton, com- 

 prising the short, deep thorax, was free from the carapace, 

 which in that region must have rested upon the muscles of the 

 back and shoulders. The number of neck and trunk vertebrae 

 combined varied in the different genera from 26 to 28, but 

 fusion had reduced the number of separate parts to 4, or at 

 most 5. Such greatly diminished flexibiUty of the back was 

 rather an advantage. The tail differed much in length in the 

 various genera, but was always massive ; the anterior vertebrae, 

 usually 7 in number, were free, the others were fused into a 

 heavy, tapering rod ; but for nearly its whole length the processes 

 of the vertebrae were very prominent, each vertebra touching 

 the tail-sheath at five points and thus giving it very effective 

 support. In ^Glyptodon the tail-vertebrae were all free. 



In most of the genera the scapula was very broad and had 

 the very long acromion common to all the edentates ; there 

 were no clavicles. The hip-bones were very pecuhar; the 

 anterior element (iliiun) stood almost vertically, at right angles 

 to the backbone, and formed a broad plate, facing forward, the 

 top of which was roughened and thickened to support the cara- 

 pace. The posterior element (ischium) was also much ex- 



