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Summary.

  • 1
    The hyomandibular, quadrate, symplectic, and styIohyoid are, in the 5 mm. stage, all one mass of cartilage.
  • 2
    This mass is fused, at this stage, to the cranial cartilage and to Meckel's cartilage.
  • 3
    The palato-pterygoid forms at about 13 mm., and grows back to meet the quadrate.
  • 4
    Until the 20 mm. stage is reached, the brain is in no place roofed over.
  • 5
    The Trabeculæ Cranii disappear between 20 mm. and 30 mm., leaving a median process, which does not join the posterior part of the skull.
  • 6
    The quadrate appears by a constriction in the hyomandibular mass.
  • 7
    The symplectic appears as a thin pointed process from beneath this mass.
  • 8
    Articulations of this mass with the cranium and with Meckel's cartilage appear at 10 mm. and 26 mm. respectively.
  • 9
    Considerable ossification is taking place at 30 mm.