﻿AND 
  AVES 
  OF 
  NORTH 
  AMERICA. 
  

  

  51 
  

  

  the 
  others 
  more 
  oval, 
  the 
  more 
  anterior 
  are 
  sub-triangular, 
  and 
  the 
  rib 
  pits 
  on 
  the 
  first 
  dorsals 
  are 
  sub-round 
  or 
  

   vertically 
  oval. 
  Thus 
  the 
  heads 
  of 
  the 
  ribs 
  also 
  vary. 
  The 
  shafts 
  are 
  all 
  flat, 
  probably 
  more 
  so 
  from 
  pressure. 
  They 
  

   are 
  frequently 
  curved 
  in 
  the 
  direction 
  of 
  the 
  compression, 
  which 
  suggests 
  a 
  vertical 
  bead. 
  They 
  however 
  are 
  probably 
  

   more 
  or 
  less 
  distorted, 
  and 
  the 
  plane 
  of 
  compression 
  changed. 
  No 
  well 
  defined 
  distal 
  extremity 
  of 
  a 
  rib 
  can 
  be 
  made 
  

   out, 
  nor 
  have 
  anything 
  like 
  abdominal 
  ribs 
  been 
  preserved. 
  

  

  The 
  scapula?' 
  arch 
  is 
  remarkable 
  for 
  its 
  large 
  clavicles 
  (or 
  procoracoids). 
  As 
  preserved, 
  the 
  latter 
  are 
  quite 
  con- 
  

   vex 
  downwards 
  both 
  antero-posteriorly 
  and 
  transversely, 
  while 
  the 
  coracoids 
  are 
  equally 
  concave 
  in 
  both 
  directions. 
  

  

  Fig. 
  7. 
  

  

  Scapular 
  Arch. 
  

   The 
  clavicles 
  have 
  a 
  remarkable 
  external 
  flat 
  projection, 
  wbich 
  is 
  separated 
  from 
  the 
  glenoid 
  cavity 
  by 
  a 
  deep 
  sinus. 
  

   The 
  glenoid 
  cavity 
  is 
  bounded 
  by 
  an 
  elevated 
  ridge, 
  which 
  sends 
  a 
  branch 
  along 
  the 
  claviculo-coracoid 
  suture 
  to 
  the 
  

   precoracoid 
  foramen. 
  This 
  foramen 
  is 
  relatively 
  of 
  small 
  size, 
  and 
  is 
  a 
  longitudinal 
  oval; 
  the 
  two 
  are 
  separated 
  by 
  

   an 
  isthmus 
  composed 
  equally 
  of 
  processes 
  of 
  clavicle 
  and 
  coracoid. 
  The 
  coracoids 
  are 
  very 
  thin 
  except 
  in 
  a 
  transverse 
  

  

  