LOXOLOPHODON AND UINTATHERIUM. 



37 



Pelvis. 



The Ilia have a great lateral expansion, with the iliac surfaces concave and 

 the gluteal nearly flat ; thin in the middle, they increase in thickness near the 

 borders, which are roughened for the attachment of the heavy oblique and 

 transverse muscles of the abdomen. The supra-iliac borders arch strongly for- 

 wards and outwards beyond the line of, and apparently below, the acetabula. 

 The acetabular borders are only slightly concave ; the prominence for the 

 attachment of the rectus muscle is low and V-shaped. The sacral surface is 

 very broad and deep, projecting beyond the sacral spines above, and roughened 

 for the attachment of the gluteal muscles. The ischial borders are deeply con- 

 cave, a muscular ridge passing horizontally across the lower surface of the ilium 

 from the margin of the acetabulum for the attachment of the gemelli muscles. 

 The ilio-lumbar angle is about i io°. The Ischia are short ; a section of them 

 as they leave the acetabulum is subtriangular. Below they expand, fan-shaped, 

 terminating in a rounded lower border and a small upward-directed tuber ischiu 

 They do not show a very strong ridge for the adductor muscles : this is what 

 we should expect from the study of the femur, which is about as rugose as that 

 of the elephant. 



The Pubes are very light, sub-cylindrical as they leave the acetabula, and 

 after this flattened in the same plane with the ischia. The pubic symphysis is 

 short. The thyroid foramina are large and oval, with their long diameters par- 

 allel to the axis of the ischia. The acetabula are large, sub-circular, and deep, 

 with prominent borders, especially the iliac, which are produced into a point ; 

 on their external extrem.ities the ischiatic are deeply notched. From the wide 

 ligamentous pit in the centre there runs a deep groove part way down the antero- 

 external side of the ischium. 



The anterior outlet of the pelvis, when compared with the pelvis of L. cor- 

 nutus, is broader and proportionately shallower. In this respect Loxolophodon 

 presents a likeness to Mastodon. The thyroid foramen is a wider oval. The ilia 

 have about the same lateral expansion and direction of the crests in both 

 genera. 



Comparison with Mastodon. The pelvis of Mastodon resembles that of Uinta- 

 therium only in general features. In an anterior view the likeness is striking, but 

 wide variations exist in the shortness of the sacral surfaces, and in the vertical di- 

 rection of the pelvis, which reduces the ilio-lumbar angle to about ioo°. Finall}'-, 

 the elongation and backward extension of the pubic symphysis contrasts with 

 the narrow symphysis of Uintatherium. 



Comparison with Rhinoceros. The ilio-lumbar angle of the pelvis of Rhinoceros 

 is less than that of Uintatherium, the pelvis having a more vertical position, as in 



