﻿FOUR 
  NEW 
  SPECIES 
  OF 
  FOSSIL 
  HORSES— 
  HAY. 
  

  

  583 
  

  

  will 
  be 
  observed 
  also 
  that 
  these 
  milk 
  molars 
  are 
  both 
  longer 
  and 
  

   narrower 
  than 
  the 
  premolars. 
  

  

  In 
  the 
  American 
  Museum 
  of 
  Natural 
  History 
  is 
  a 
  lower 
  jaw 
  of 
  a 
  

   young 
  horse 
  which 
  the 
  writer 
  refers 
  to 
  Equus 
  niohrarensis. 
  It 
  was 
  

   found 
  at 
  Hay 
  Springs, 
  with 
  the 
  other 
  remains 
  obtained 
  there. 
  In 
  

   this 
  jaw 
  there 
  are 
  present 
  the 
  three 
  milk 
  molars 
  (fig. 
  23) 
  and 
  the 
  

   anterior 
  two 
  permanent 
  molars. 
  The 
  second 
  of 
  these 
  is 
  little 
  worn. 
  

   The 
  first 
  permanent 
  incisors 
  had 
  not 
  yet 
  begun 
  to 
  wear 
  and 
  the 
  

   others 
  are 
  missing 
  from 
  the 
  specimen. 
  The 
  specimen 
  is 
  to 
  be 
  com- 
  

   pared 
  with 
  a 
  jaw 
  of 
  similar 
  age 
  described 
  here 
  under 
  E. 
  excelsus 
  

   (fig. 
  24). 
  

  

  W 
  24 
  

  

  • 
  I 
  

  

  VS 
  

  

  Figs. 
  22-24.-22, 
  Equxts 
  niobrakknsis. 
  x 
  §. 
  Amee. 
  Mus. 
  Nat. 
  Hist. 
  Eight 
  

  

  inrER 
  MILK 
  MOLARS. 
  23, 
  LEFT 
  LOWER 
  MILK 
  MOLARS. 
  2758, 
  AMEE. 
  MUS. 
  NAT. 
  

  

  Hist. 
  24, 
  Equxts 
  excelsus. 
  X 
  §. 
  Left 
  lower 
  milk 
  molars. 
  2758, 
  Amer. 
  

   Mus. 
  Nat. 
  Hist. 
  

  

  Dimensions 
  of 
  the 
  jaw 
  and 
  teeth 
  of 
  No. 
  2757, 
  A. 
  M. 
  N. 
  H. 
  

  

  mm. 
  

  

  Length 
  from 
  front 
  of 
  jaw 
  to 
  rear 
  of 
  the 
  ascending 
  ramus 
  parallel 
  with 
  the 
  teeth 
  . 
  . 
  460 
  

  

  Length 
  of 
  the 
  symphysis 
  95 
  

  

  Height 
  in 
  front 
  of 
  first 
  milk 
  molars, 
  dm.2 
  72 
  

  

  Height 
  in 
  rear 
  of 
  third 
  milk 
  molars, 
  rfw.^ 
  90 
  

  

  Height 
  of 
  condyle 
  above 
  the 
  surface 
  on 
  which 
  the 
  jaw 
  rests 
  235 
  

  

  Length 
  of 
  the 
  space 
  between 
  last 
  incisor 
  and 
  first 
  milk 
  molar, 
  dm.^ 
  82^ 
  

  

  First 
  milk 
  molar, 
  length 
  40 
  

  

  First 
  milk 
  molar, 
  width 
  16 
  

  

  Second 
  milk 
  molar, 
  length 
  32 
  

  

  Second 
  milk 
  molar, 
  width 
  15. 
  5 
  

  

  Third 
  milk 
  molar, 
  length 
  33. 
  5 
  

  

  Third 
  milk 
  molar, 
  width 
  15 
  

  

  First 
  true 
  molar, 
  length 
  33 
  

  

  First 
  true 
  molar, 
  width 
  13 
  

  

  