Referring back to the foregoing table. The development of tushes may be an adaptive character; but in the elephants it is inc. 2 of the upper and inc. 2 of the lower jaw which are so developed. In _Pyrotherium_, in the upper dentition, it is also inc. 2 which makes the tush, and inc. 1 is enlarged as in _Moeritherium_, and, so far as we know, has not been reduced in later forms as it was in the elephant line. In the lower jaw we have no final evidence which will show whether it is inc. 1 or inc. 2 which makes the tush; but the lower tush bites against upper inc. 2 and I have considered it to be incisor 2. The loss of the teeth behind the tushes is a character to be expected in the development of tushes and gives no data. The bilophodont character of the back teeth has occurred many times in the animal kingdom and while it may be the inheritance of the early elephants it can not be used as an argument. The position of the nasal opening looks very much like that of elephants, but again is coincident with the development of a proboscis. However, this has not occurred a great number of times in the animal kingdom, and where it has, it takes a variety of forms of modification. In _Pyrotherium_, the modification is of the type in elephants, and elephants only. A very striking feature is the development of the dental region downward so that the basicranial axis is bent upward, making an angle of about 140 degrees. There are other cases of the bending of the basicranial axis; but in the other ungulates it is a bend downward, the reverse of what we find here and in elephants. To adjust the posterior part of the nasal chamber to this, the pterygoids and the alisphenoids are developed into great wing-like plates on either side. I find this modification of the basicranial axis and of the palatal, pterygoid and alisphenoid bones in no other group but the elephants. In _Palaeomastodon_ it has been developed to a degree so that the angle is about 155 degrees. The back of the palatine bones is also characteristic, for these begin as narrow pointed bones and behind the last molar expand into wide plates, just as in _Palaeomastodon_ (and in no other groups), having the postpalatine foramen opposite or behind the last molar. The post-tympanic region of the squamosum is modified so that this process unites with the anterior squamosal region to crowd out more or less completely the tympanic bone where it should surround the auditory meatus. This feature is common to the elephants, the hyracoids, and the toxodonts, so that I consider it a primitive feature indicative of the ultimate common ancestry of these groups. The tympanic bulla can be compared with that of elephants closely, and has much in common with that of toxodonts, but in this last group the tympanic is much more highly developed.