iyo 



PATAGONIAN EXPEDITIONS I PALAEONTOLOGY. 



(10) The pelvis is fully known only in the Megalonychidce, in which it 

 is very constant and has considerable resemblance to that of the modern 

 Tardigrada. The ilium has a short, stout peduncle and a large anterior 

 plate, which extends well in front of the sacrum ; the acetabular border is 

 external, the ischial and pubic borders internal, in consequence of which 

 the broad gluteal surface has an almost dorsal position and the iliac sur- 

 face presents ventrally ; there is no such expansion and eversion of the 



FIG. 21. 

 Hapalops ruetimeyeri, pelvis from the ventral and right sides, x \. 



ilium as is seen in Megatherium and Mylodon, a change which invariably 

 accompanies great increase in stature and in the bulk of viscera to be 

 supported. 



The ischium is very short antero-posteriorly and its dorsal portion is 

 stout, but the tuberosity is small ; the descending process is long and 

 slender and the ischium thus encloses two sides of the very large obtura- 

 tor foramen, the principal diameter of which is dorso-ventral ; the sacro- 

 sciatic foramen is much smaller than in the later types and its longer axis 

 is antero-posterior. The pubis is elongate, slender and subcylindrical, 

 except near the distal end, where it becomes compressed and plate-like ; 

 the short symphysis is formed by both pubes and ischia; near the proximal 

 end of the pubis is in some species a low rugose process, corresponding to 

 that in the glyptodonts. The great dorso-ventral extension of the pubes 

 and ischia, though less exaggerated than in some of the Pleistocene genera, 

 makes the pelvic opening very large in this diameter. The acetabulum 



