CHAPTER XIII. 



CLASS MAMMALIA.* 



Warm-hlooded hairy animals with double occipital condyle., a 

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

 nucleated red blood-corpuscles, and mammary glands with which 

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

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

 always {except in Monotremeata) open into the bladder. 



In addition to the characters mentioned in the definition 

 which absoluteij^ characterise the Mammaha, we may mention 

 the following which are almost liniversally present. 



Tlie external auditory meatus is tubular and its opening is 

 almost ahvays 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 tvm- 



* 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. Geoffroy St. Hilaire et F. Cuvier, Histoire Natu- 

 relle des Mammiferes, 'ParislS-iO-io. A. E. Brehm., Illustrirtes Thierlehen, 

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

 Vertebrata, London, 187 1. Flower, Osteology of the Mammalia, 3rd ed. 1885. 

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

 Mammalia, vol. 10 of the Cambridge Natiiral History', 1902. R. 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, JFIandbuch der 

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

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

 bridge, 1898. F. ]\1. Balfour. .4 Treatise on Comparative Embryology, 

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

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



