HISTORY OF THE fASTRAPOTHERIA 511 



The skull was extremely peculiar, more so than in any other 

 of the contemporary genera of hoofed animals. The toothless 

 premaxillaries were quite small, but thick, and must have sup- 

 ported an elastic pad, against which the lower incisors could 

 effectively bite in cropping herbage. The nasal bones were 

 extremely short and there must have been a proboscis or greatly 

 inflated snout, probably the former ; the immense develop- 

 ment of sinuses in the frontal bones elevated the whole fore- 

 head into a great, dome-like convexity, a feature which is not 

 equalled in any other known mammal. The orbits were open 

 behind and the brain chamber was small, so that the sagittal 

 and occipital crests were very high and strong, to afford suffi- 

 cient surface for the attachment of the great temporal muscles. 

 The horizontal portion of the lower jaw was shallow vertically, 

 but very thick and massive, and the symphyseal region was 

 broad and depressed. 



Unfortunately, the skeleton is still very incompletely 

 known. Of the vertebrae, only the atlas and axis have been 

 recovered, and these resembled those of the Santa Cruz ftoxo- 

 dont \Nesodon, on a larger scale. The scapula had a very 

 thick spine, without the projections which were found in most 

 of the Santa Cruz ungulates. The limb-bones were long and 

 comparatively slender, and the processes for muscular attach- 

 ment were singularly small and weak ; the bones of the fore- 

 arm and lower leg did not codssify and were proportionately 

 elongate, the tibia being but little shorter than the femur. 

 The latter had the flattened shaft which recurs in nearly all of 

 the very heavy ungulates, but retained a remnant of the third 

 trochanter. If the feet found isolated in the Santa Cruz and 

 Deseado stages have been correctly referred to this order, then 

 the genus was five-toed and the feet were broad, short and 

 heavy, quite elephantine in appeamnce, especially the fore 

 foot. The ankle-joint was very peculiar and the calcaneum had 

 no articulation with the fibula, which it had in all the other 

 indigenous South American ungulates. 



