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Summary.

  • 1
    The chondrocranium and bony skull are described in five stages of development of Ornithorhynchus.
  • 2
    It is shown (p. 17) that Ornithorhynchus provides an intermediate condition between reptiles and higher mammals, representing a mosaic of characters some of which are typically reptilian and others equally typically mammalian.
  • 3
    Ornithorhynchus is definitely a mammal which has preserved a number of reptilian characters.
  • 4
    The pleurocentrum of the proatlas verterba fuses with that of the atlas vertebra, and forms part of the odontoid peg, as in Lacertilia, Rhynchocephalia, and higher mammals.
  • 5
    The cochlear capsule is not formed out of cartilage of the basal plate (contra Gaupp).
  • 6
    The dumb-bell bone probably ossifies independently of the palatal processes of the premaxillæ, and represents the prevomers (supporting Wilson and Broom).
  • 7
    The “mammalian pterygoid” of Ornithorhynchus is the detached lateral wing of the parasphenoid of reptiles and the dorsal plate of the pterygoid of higher mammals.
  • 8
    The “Echidna-pterygoid” is the pterygoid of reptiles and the secondary pterygoid cartilage (and subsequent ossification therein) of higher mammals.
  • 9
    The alisphenoid is present in Ornithorhynchus as a perichondral ossification in the ala temporalis.