112 



PATAGONIAN EXPEDITIONS: PAL/EONTOLOGY. 



the widely open orbits, the relatively high and erect occiput, and the dis- 

 tinct occipital and sagittal crests. There is no such development of air- 

 sinuses and, in consequence of the less exaggerated height of the teeth, 

 the ascending ramus of the mandible is much lower. A partial exception 

 to this description is afforded by the skull of Metopotoxus, in which the 

 occipital plane has a decided forward inclination and the rostrum is short- 

 ened and directed steeply downward, much as in Panochthiis. 



Despite the above-mentioned differences, however, the glyptodont 

 nature of the skull in these Santa Cruz genera is apparent at the first 



FIG. 12. 



Bones of left fore-limb of glyptodonts, x \. a. Glyptodon asper (after Burmeister) . 

 palaoJioploplwrus australis. 



b. Pro- 



glance, and the characteristic descending suborbital process from the zygo- 

 matic arch is already a most striking feature. 



8. The vertebral column has nearly, but not quite, attained to the de- 

 gree of concentration found in the later genera of the group. The neck is 

 very short ; the atlas is free, but the axis and the three succeeding cervi- 

 cals (in Metopotoxus only two) are fused into a compound bone ; the sixth 

 again is free, while the last cervical, first and second thoracics have coa- 

 lesced. Two or three of the succeeding thoracic vertebrae are separate, 



