E. L. Troxell — Amynodonts in Marsh Collection. 23 



larynx and windpipe while the mouth is open under water 

 as in the act of gathering food. 



An intijnate connection of the epiglottis with the 

 pharynx, as enclosed by the soft palate, is seen in the 

 modern horse, where no passage of air is possible through 

 the mouth in ordinary breathing. In this recent animal, it 

 is thought to be a provision against breathing the dust 

 from the grasses which constitute a greater part of its 

 food. There is a resemblance in the form of this opening 

 in the amynodonts and in the horse. 



A further adaptation to a watery habitat is seen in the 

 forward and high position of the orbits, which serves to 

 keep the periscopic eyes out of the water for swimming or 

 for observation while hiding ; this finds its greatest devel- 

 opment in Hippopotamus, in which the orbits actually 

 rise above the plane of the face, and here also, as well as 

 in Metamynodon, we find the broad spreading feet suited 

 for walking on the softer ground near and in rivers and 

 lakes — feet which are so constructed that the toes fold 

 together backward as they are lifted and carried forward 

 through the resisting water. 



In speaking of the hippopotamus, Roosevelt and Heller 

 say that the semi-aquatic habits have favored its develop- 

 ment to an enormous bulk. This is no doubt true of 

 Metamynodon also, and while locomotion would be diffi- 

 cult and clumsy on the land, it would be greatly facili- 

 tated by the buoyancy of water even if the beast were only 

 partly submerged. 



In both the genera of the Amynodontidae the skulls 

 show fossae in the roof of the mouth, the purpose of which 

 is problematical; but together with the deep antorbital 

 depressions, they certainly constricted the nasal passages 

 to a considerable degree and must have interfered with 

 the organs of smell — of minor importance to an aquatic 

 beast. 



The following points may be interpreted as evidence of 

 a prehensile lip at least in Metamynodon: (1) the rough- 

 ened supra-orbital ridges, together with the conspicuous 

 tubercles just in front of the eyes, and (2) the large cheek 

 depressions, possibly indicative of large face muscles; 

 (3) the moderately large infra-orbital foramina, doubled 

 in the holotype of A. erectus, and required in order to 

 furnish plentiful nourishment and nerves to the facial 

 organs; and finally (4) the nature of the narial opening 



