Barbour — Lig amentum Teres in Nebraska Proboscidea. 251 



Aet. XY. — Evidence of the Ligamentum Teres in Nebraska 

 Proboscidea • by Ekwin H. Bakbottk. 



Incidental reference was made in this Journal"* to the round 

 ligament of Nebraska proboscideans as evidenced by specimens 

 in the collections of the Nebraska State Museum. However 

 the subject seems to be worthy of more than passing mention. 

 Comparison of acetabula of our various mastodons and mam- 

 moths lead to the conclusion that absence of the round liga- 

 ment is not properly a character of the Proboscidea. From 

 evidence at hand it appears that the round ligament may have 

 been present in all of our Proboscidea. In some it seems to 

 have been large and functional. This is true particularly in 

 the case of the longirostral mastodons of the Pliocene of North- 

 ern Nebraska, and to a degree in the case of some of the 

 brevirostral forms from the Pleistocene. Femur heads of the 

 former show deep and unmistakable ligamentous scars, while 

 those of the latter show little if any. 



In the case of brevirostral mastodons from our Pleistocene, 

 reduction of the round ligament is evident. Still even here 

 the fossae are long, broad, and relatively shallow though 

 occasionally deep. The femur heads of some mastodons show 

 slight scars, and roughened areas for attachment, although the 

 bulk of them are smooth as in Mastodon americanus. As for 

 mammoths the fossae are long, broad, and in certain instances, 

 surprisingly deep. In one case, at least, the fossa is not only 

 relatively but actually broader, longer, and deeper than in the 

 early longirostral forms. However the femur heads of mam- 

 moths seem to be as free from scars as those of modern ele- 

 phants. Obliteration of the acetabular fossa was a slow process 

 judging by the specimens at hand, which range from the Pli- 

 ocene and Pleistocene to the present. In none is the fossa 

 filled by osseous growth as in the modern elephant. All this 

 seems to be morphological rather than coincidental. Nebraska 

 seems to be singularly rich in proboscidean remains. Four 

 mammoths and at least twice as many mastodons have already 

 been described and many more are destined to be added to the 

 list. 



The " tetrabelodon beds " of Nebraska extend along the 

 northern tier of counties from Knox through Sioux, a distance 

 of some 300 miles. 



In the case of the Boyd County Tetrabelodon the acetabular 

 fossa is deep and large. This is a new and undescribed Tetra- 



* Barbour, Erwin H., A New Longirostral Mastodon, Tetrabelodon lulli, 

 this Journal, vol. xxxix, p. 87, Jan., 1915. 



