﻿1104 
  Forty-seventh 
  Report 
  on 
  the 
  State 
  Museum. 
  

  

  pods 
  there 
  are 
  internal 
  structures 
  which 
  seem 
  to 
  have 
  served 
  

   similar 
  functions 
  to 
  the 
  spondylium 
  and 
  cruralium 
  of 
  the 
  

   Articulates. 
  These 
  occur 
  in 
  the 
  genera 
  Lingulasma, 
  Teimeeella, 
  

   Dinobolus, 
  and 
  all 
  the 
  genera 
  constituting 
  the 
  group 
  termed 
  by 
  

   Davidson 
  and 
  Kino, 
  the 
  Trimerellidje', 
  and 
  have 
  been 
  known 
  

   as 
  the 
  platforms. 
  Though 
  all 
  these 
  structures 
  have 
  manifestly 
  

   subserved 
  the 
  same 
  purpose 
  to 
  the 
  animal 
  their 
  origin 
  is 
  due 
  to 
  

   unlike 
  causes 
  though 
  their 
  growth 
  was 
  aided 
  by 
  similar 
  con- 
  

   ditions 
  ; 
  hence 
  they 
  are 
  not 
  strictly 
  homologous 
  parts. 
  

  

  The 
  spondylium 
  is 
  an 
  area 
  of 
  muscular 
  implantation. 
  It 
  is 
  

   derived 
  from 
  the 
  convergence 
  and 
  coalescence 
  of 
  the 
  dental 
  

   lamellae 
  and 
  forms 
  a 
  receptacle 
  primarily 
  for 
  the 
  proximal 
  por- 
  

   tion 
  of 
  the 
  pedicle 
  and 
  for 
  the 
  capsular 
  or 
  pedicle-muscles 
  and 
  

   eventually 
  for 
  all 
  the 
  muscles 
  attached 
  to 
  the 
  valve. 
  For 
  the 
  

   inception 
  of 
  the 
  platform 
  on 
  the 
  pedicle-valve 
  of 
  the 
  Trimer- 
  

   ellids 
  it 
  is 
  not 
  so 
  easy 
  to 
  assign 
  an 
  explanation, 
  but 
  its 
  beginning 
  

   once 
  made, 
  there 
  seems 
  no 
  reason 
  to 
  doubt 
  that 
  the 
  increase 
  in 
  

   size 
  and 
  prominence 
  both 
  of 
  platform 
  and 
  spondylium 
  has 
  been 
  

   greatly 
  aided 
  by 
  the 
  crowding 
  of 
  the 
  essential 
  organs 
  of 
  the 
  

   animal 
  about 
  and 
  beneath 
  these 
  muscular 
  plates 
  (see 
  pp. 
  193, 
  

   194). 
  

  

  Considering 
  the 
  spondylium 
  in 
  its 
  elementary 
  condition 
  where, 
  

   as 
  in 
  Orthis, 
  it 
  is 
  represented 
  only 
  by 
  the 
  convergent 
  dental 
  

   plates 
  uniting 
  with, 
  or 
  resting 
  upon 
  the 
  bottom 
  of 
  the 
  valve, 
  

   enclosing 
  only 
  the 
  base 
  of 
  the 
  pedicle 
  and 
  its 
  muscles, 
  it 
  becomes 
  

   evident 
  that 
  the 
  plate 
  is 
  actually 
  but 
  a 
  modification 
  of 
  the 
  

   original 
  pedicle-sheath. 
  It 
  is 
  the 
  inner 
  moiety 
  of 
  this 
  sheath 
  

   surrounding 
  the 
  pedicle, 
  which 
  has 
  become 
  involved 
  in 
  or 
  

   enclosed 
  by 
  the 
  growth 
  of 
  the 
  pedicle- 
  valve, 
  and 
  further 
  modified 
  

   by 
  the 
  development 
  of 
  articulating 
  processes 
  where 
  it 
  comes 
  in 
  

   contact 
  with 
  the 
  brachial 
  valve. 
  It 
  may, 
  therefore, 
  be 
  inferred 
  

   that 
  wherever 
  the 
  spondylium 
  is 
  present, 
  whether 
  in 
  the 
  incipient 
  

   condition 
  or 
  in 
  the 
  more 
  advanced 
  stage 
  of 
  development 
  

   in 
  which 
  it 
  supports 
  all 
  the 
  muscles 
  of 
  the 
  valve, 
  it 
  is 
  

   or 
  has, 
  at 
  some 
  period 
  of 
  growth, 
  been 
  accompanied 
  by 
  the 
  exter- 
  

   nal 
  portion 
  of 
  the 
  sheath 
  which 
  is 
  termed 
  the 
  deltidium. 
  Thus 
  

   the 
  spondylium 
  appears 
  to 
  be 
  but 
  the 
  complement 
  of 
  the 
  del- 
  

   tidium, 
  and 
  that 
  the 
  two 
  were 
  together 
  included 
  in 
  the 
  original 
  

  

  162 
  

  

  