[108] This is Gadow's view; according to Huxley the quadrate forms the malleus; according to Baur it forms the zygomatic process of the squamosal, and according to Broom the interarticular mandibular cartilage.
[109] According to Leche, Morphol. Jahrb. XIX. p. 502, the molar teeth belong morphologically to the first series, i.e. they are milk teeth without vertical successors.
[110] The researches of Bateson, P.Z.S. 1892, p. 102, have shown that cases of individual variation in the number of teeth are common.
[111] Baur, however, suggests (Anat. Anz. vol. IV. 1889), that a tibial sesamoid found in Procavia, many rodents, edentates and Ornithorhynchus is a vestigial tibiale, and that the astragalus is the intermedium.
[112] This perforation of the acetabulum in Echidna is a secondary character occurring late in development, and consequently is not of phylogenetic importance.
[113] See R. Owen, "Monograph of the Fossil Mammalia of the Mesozoic Formation," Pal. Soc. Mon. 1871.
H.F. Osborn, "Structure and Affinities of Mesozoic Mammals," J. of Philad. Acad. 1888, vol. IX.
O.C. Marsh, "Jurassic Mammals," Amer. J. Sci. 1878 et seq.
[114] See Oldfield Thomas, Brit. Mus. Cat. of Marsupialia and Monotremata (1888).
[115] W. Kükenthal, Anat. Anz. VI. p. 364, 1891. C. Röse, Anat. Anz. VII. p. 639.