CHAPTER XIII. 



CLASS MAMMALIA.* 



Warm-blooded hairy animals with double occipital condyle, a 

 heart with two ventricles and two auricles, a left aortic arch, non- 

 nucleated red Mood-corpuscles, and mammary glands with which 

 they suckle their young. The lower jaw consists of a single piece 

 on each side and articulates ivith the squamosal, and the ureters 

 always (except in Monotremeata) open into the bladder. 



In addition to the characters mentioned in the definition 

 which absolutely characterise the Mammalia, we may mention 

 the following which are almost universally present. 



The external auditory meatus is tubular arid its opening is 

 almost always marked by a fold of skin called the pinna. There 

 are three ossicles, the malleus, incus and stapes, connecting the 

 tympanic membrane with the fenestra ovalis. The cochlea is 

 spirally coiled. The retina contains blood-vessels. The 'tym- 



* J. C. D. v. Schreber, Die Sdugethiere in Abbildungen nach der Natur 

 mit Beschreibungen, fortgesetzt von J. A. Wagner, 1-7, and sup: 1-5, 

 Leipzig 1775-1855. E. Geoffrey St. Hilaire et F. Cuvier, Histoire Natu- 

 relle des Mammiferes, Paris 1840-45. A. E. Brehm., Illustrirtes Thierleben, 

 1-3. De Blainville, Osteographie, 1835-54. Huxley, Anatomy of the 

 Vertebrata, London, 1 871. Flower, Osteology of the Mammalia, 3rd ed. 1885. 

 Flower & Lydekker, Mammals living and extinct, London, 1891. Beddard, 

 Mammalia, vol. 10 of the Cambridge Natural History, 1902. K. Owen, Odon- 

 tography, 2 vols., London, 1840-45. Tomes, Dental Anatomy, 5th ed., 

 London, 1898. Wallace, Geographical Distribution of Mammals, 2 vols. 

 London, 1876, and Island Life, London, 1880. W. L. & P. L. Sclater, 

 The Geography of Mammals, London, 1899. Lydekker, Geographical 

 History of Mammals, Cambridge, 1896. Trouessart, Catalogus Mamma- 

 Hum tarn viventium quam fossilium, Berlin, 1897. Zittel, Handbuch der 

 Palaeontologie, vol. 4, Leipzig, 1891-3, and Grundzuge der Palaeontologie, 

 Leipzig, 1895. Woodward, Outlines of Vertebrate Palaeontologie, Cam- 

 bridge, 1898. F. M. Balfour, A Treatise on Comparative Embryology, 

 vol. 2, London, 1882. C. S. Minot, Human Embryology, New York, 1892. 

 A. M. Marshall, Vertebrate Embryology, London, 1893. 



