﻿E. 
  L. 
  Troxell 
  — 
  A 
  Tiny 
  Oligocene 
  Artiodactyl. 
  393 
  

  

  Doctor 
  Matthew 
  has 
  figured 
  and 
  described 
  the 
  limb 
  and 
  

   foot 
  bones, 
  and 
  it 
  is 
  evident 
  that, 
  in 
  modernization, 
  the 
  

   teeth 
  and 
  skull 
  are 
  much 
  in 
  advance 
  of 
  the 
  evolution 
  of 
  

   the 
  foot 
  structure. 
  The 
  third 
  and 
  fourth 
  metatarsals 
  are 
  

   distinct, 
  but 
  appressed 
  (they 
  may 
  co 
  ossify 
  with 
  age) 
  ; 
  in 
  

   other 
  words, 
  there 
  is 
  no 
  cannon-bone 
  even 
  in 
  the 
  hind 
  

   foot, 
  which 
  is 
  always 
  the 
  more 
  progressive. 
  Although 
  

   the 
  lateral 
  metatarsals 
  II 
  and 
  V 
  are 
  very 
  slender 
  and 
  

   thread-like, 
  they 
  are 
  complete, 
  yet 
  the 
  pes 
  is 
  functionally 
  

   didactyl. 
  The 
  cuboid 
  and 
  navicular 
  are 
  coossified, 
  like- 
  

   wise 
  the 
  radius 
  and 
  ulna, 
  and 
  the 
  tibia 
  and 
  fibula. 
  

  

  Several 
  specimens 
  are 
  represented 
  in 
  the 
  Marsh 
  Col- 
  

   lection, 
  mostly 
  fragments 
  of 
  the 
  lower 
  jaws 
  or 
  of 
  maxil- 
  

   laries, 
  out 
  of 
  which 
  two 
  specimens 
  in 
  particular 
  will 
  be 
  

  

  Fig. 
  1. 
  

  

  Fig. 
  1. 
  — 
  Skull 
  and 
  ramus 
  of 
  Hypisodus 
  alacer, 
  sp. 
  nov. 
  Holotype. 
  Cat. 
  

   No. 
  10033, 
  Yale 
  Fossil 
  Vertebrate 
  Collection. 
  Natural 
  size. 
  

  

  described, 
  one 
  the 
  skull 
  and 
  ramus, 
  the 
  other 
  a 
  maxillary 
  

   bone 
  with 
  the 
  tooth 
  series 
  complete 
  from 
  the 
  third 
  pre- 
  

   molar 
  backward. 
  

  

  Hypisodus 
  alacer, 
  sp. 
  nov. 
  

   (Figs. 
  1-3.) 
  

  

  Of 
  the 
  holotype, 
  Cat. 
  No. 
  10033, 
  Yale 
  Fossil 
  Verte- 
  

   brate 
  Collection, 
  the 
  skull 
  and 
  lower 
  jaws 
  alone 
  were 
  pre- 
  

   served, 
  and 
  of 
  these 
  the 
  anterior 
  parts 
  are 
  entirely 
  gone. 
  

   The 
  skull 
  is 
  short 
  and 
  broad, 
  the 
  orbit 
  large, 
  and 
  the 
  otic 
  

   bullas 
  so 
  inflated 
  that 
  they 
  occupy 
  over 
  a 
  third 
  of 
  the 
  ver- 
  

   tical 
  height 
  of 
  the 
  skull. 
  They 
  seem 
  to 
  have 
  had 
  no 
  can- 
  

   cellous 
  tissue, 
  are 
  separated 
  widely 
  posteriorly, 
  but 
  in 
  

   front 
  are 
  closely 
  in 
  contact. 
  The 
  external 
  auditory 
  me- 
  

   atus, 
  situated 
  well 
  forward, 
  opens 
  at 
  an 
  angle 
  of 
  45° 
  

   toward 
  the 
  rear 
  and 
  is 
  very 
  large, 
  having 
  a 
  diameter 
  

  

  