PYROTHERHM 159 



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 Moeritheriutn, 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 oc- 

 curred 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 devel- 

 opment 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 Py- 

 rotherium, 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 basi-cranial 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 ptery- 

 goids 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 alis- 

 phenoid bones in no other group but the elephants. In 

 Palacomastodon 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 



