358 



H. S. Lull — Pleistocene Ground Sloth, 



mina for the exit of the posterior branches of the sacral nerves 

 which lie on either side of the spinous crest. 



These are somewhat variable in their size and not equidistant 

 in their spacing. Between sacrals two and three there arises 

 a second series of apertures on either side, the smaller addi- 

 tional foramina being without and somewhat in advance of the 

 others. From the third sacral onward the apertures of the 

 outer series increase rapidly in size and replace the original row, 

 which entirely disappears. At the sixth sacral these foramina 

 merge with the intervertebral foramina for the exclusive exit 

 of the sacral nerves. This occurs opposite the large sacro- 

 ischiadic foramen of the innominate bone. The relative regu- 



Fig. 10. 



Fig. 10. Pelvis of Mylodon harlani, No. 10264, Yale collection, viewed 

 from above. One-twelfth nat. size, ac, acetabulum ; ob, obturator fora- 

 men ; pb, pubis. 



larity and size of these foramina would seem to distinguish the 

 Texan Mylodon from the specimen of M. robustus described 

 by Sir Richard Owen, if one may judge from his published 

 figures of the pelvis.* 



Innominate bones. — Although in reality part of the appen- 

 dicular skeleton, it is most convenient to describe these ele- 

 ments at this place in connection with the sacrum. The entire 

 pelvis, No. 10264, is slightly larger than that of M. robustus 

 described by Owen, the dimensions of which are : greatest 

 width 3 feet 5 inches, antero-posterior diameter of ilium, 1 

 foot 6 inches. These measurements in the present specimen 

 are 3 feet 6 inches and 1 foot 7 inches respectively. The ilium 

 is rounded anteriorly, the labium or anterior margin being 

 deflected anteriorly in such a way as to be broadly convex 

 upward and concave on its under anterior face. From the 

 -Owen, E., pi. 10, 1842. 



