HISTORY OF THE JAMBLYPODA 455 



exaggerated and were most striking in the terminal genus of 

 the series, '\Eobasileus. 



(4) Unfortunately, nothing is yet known of the skeleton 

 of jBaihyopsis and '\E lac hoc eras, so that it is not practicable 

 to follow out all the stages of skeletal modification, though the 

 general course of development is sufficiently plain. The neck 

 did not change greatly, except to become very strong and heavy 

 and to grow shorter proportionately as the skull was lengthened. 

 The body remained long throughout the series, but gained 

 greatly in bulk, as the stature of the animal increased. 



(5) The limb-bones lost their primitive character, such as 

 the epicondylar foramen of the humerus and the third tro- 

 chanter of the femur, and then, with the great increase of the 

 weight to be supported, the marrow-cavities were filled with 

 spongy bone and the hip-bones increased enormously in width ; 

 the femur lost its cylindrical shape and was flattened antero- 

 posteriorly, which gave it a very elephantine appearance. 

 None of the limb-bones was suppressed or greatly reduced in 

 size, nor was there any coossification between them. 



(6) The feet early gained their definitive character ; at 

 no time was there any loss of digits, but the originally divided 

 toes were, in the genera of the Wasatch and subsequent stages, 

 united into the columnar foot, and the hoofs were reduced from 

 their primitively pointed shape to nodular form. 



As in the Proboscidea, therefore, there was comparatively 

 little change in the skeleton after the massive and bulky pro- 

 portions had been acquired, but great and continual modifica- 

 tion of the skull. At the time when the fAmblypoda finally 

 disappeared, no ungulate had acquired the hypsodont dentition. 

 Had the group survived till the middle Miocene, a time when 

 the spread of grassy plains so profoundly affected the feeding 

 habits of many herbivorous mammals, the high-crowned teeth 

 might have been developed in them also, and this, in turn, 

 would have produced other changes in the skull, making closer 

 the parallel with the Proboscidea. 



