The depth of the symphysis pubis, and the oblique forward direction of the transverse processes in the lumbar region, are points probably correlated functionally with the strength of the hind limbs. The large size of the abdominal relatively to the thoracic cavity may be connected with the multiparous character of the order generally. The spine of the second dorsal vertebra has a small ossicle articulated to its apex, and pointing forward, much as in the long-necked grazing mammals the ligamentum nuchae is placed along the dorsal and cervical regions. The two first cervical vertebrae are, as is usual in mammals, much the largest in the series, and they contrast, as in all placental mammals, with the other cervical and also with all the other moveable vertebrae, in having, when adult, the centre of the first fused with that of the second, and in being connected with each other and the skull by cartilages and synovial membranes without fibro-cartilaginous discs. The first rib has its head articulated to the bodies, and its tubercle to the transverse processes of both the last cervical and the first dorsal vertebra.
There are two lateral episternal bones between the first of the six sternal bones, the so-called 'manubrium' and the clavicle, one on each side, but there is no central cervical prolongation of the sternum as in Lepus.
In the carpus there is the same number of bones as in that of man, for though the scaphoid and lunar are fused into one bone, the scapho-lunar, as they are also in Carnivora and Chiroptera, a bone, the os centrale, exists between it and the os trapezium, os trapezoides, and os magnum in the second row of carpals, which is not represented by a distinct bone in the human carpus, nor in those of Ungulata, Cetacea, Chiroptera, Edentata, Marsupialia, and Monotremata, but only in those of Rodentia, Insectivora, and Simiadae exclusively of the Chimpanzees. As in all mammals, though in no amphibian a single bone, the os unciforme, supports the two outer metacarpals. In this enumeration the ulnar sesamoid bone, or 'os pisiforme,' is not reckoned as a carpal bone, nor any bone of similar function in connection with the tendons on the volar side of the hand.
In Rodentia we find two more bones in the tarsus than in the human subject, the os scaphoides being double, and an accessory bone present on the inner side of the inner os cuneiforme.
For general anatomy, Krause, Die Anatomie des Kaninchens, Leipzig, 2nd ed., 1884; and T. J. Parker, Zootomy, London, 1884, p. 301.
For an account of the position of the anticlinal vertebra in the order Rodentia and elsewhere, see Giebel, Beitr'age zur Osteologie der Nagethiere, 1857, p. 35, or Abhandl., Nat. Verein fur Sachsen und Thuringen, i. p. 223, ibique citaia; or Die Saugethiere, 2nd ed. 1859, p. 6.
For the general characteristics of Mammalian vertebrae, see Professor Owen, Descriptive Catalogue of the Osteological Series of the Royal College of Surgeons, vol. i. pp. 7,8, I853.
For the nomenclature of the several elements of a vertebra, ibid. p. xliv.
For the Pro-atlas of Amniota, see Albrecht. Z. A. iii. 1880; and Bull. Mus. Roy. d'Hist. Nat. Belg. ii. 1883.
For the Osteology of the Rodentia, see Cuvier's Ossemens Fossiles, 2nd ed., 1823, vol. v. pt. i. pp. 4, 14, 44. Waterhouse, Mag. Nat. Hist., N. S., vol. iii. 1839, A. N. H. 1841, 1842, takes the conformation of the lower jaw and of the anterior portion of the zygomatic arch as furnishing a basis for classifying the order in the three sections, Murina, Hystricina, and Leporina. In Johnston's Physical Atlas, 1856, ad PL. 28, he divides the order into four families, Muridae, Sciuridae, Hystricidae, and Leporidae. See H. N. Turner, P. Z. S. 1848, p. 63. J. F. Brandt, Untersuchungen fiber d. craniologisch. Entwickelungstufen der Nager d. Jetztzeit, M^moires de l'Acade'mie Imp. des Sciences de Saint Petersbourg, ser. vi. torn. vii. pp. 127-336, 1855, laying weight (p. 141) on the form and general contour of the brain-case, the characters of the base of the cranium, the direction of the pterygoid processes, the conformation of the palate with the foramina incisiva, and of the ossa lacrymalia, divides the order Rodents s.
Glires into four suborders, Myomorphi, Sciuromorphi, Hystricomorphi, and Lagomorphi. For later views, see E. R. Alston, P. Z. S. 1875, 1876, and infra, pp. 43-45.
For the resemblances between the skeleton of the Rodents and that of the Elephant, see Cuvier, l. c. i. pp.10-12.
For the differences between the skeleton of the Rodents and that of the Aye Aye, Chiromys Madagascariensis, see De Blainville, Osteographie, Fasc. iii. 1841; Professor Owen, Tr. Z. S. v. 1863, pp. 79-83; Professor Peters, Berlin Abhandl. for 1865, pp. 89-92.
For the microscopic characters of the teeth of the Rodents, and their classi-ficatory value, see J. Tomes, Ph. Tr. 1850, pp. 553-561, and C. S. Tomes, Manual of Dental Anatomy, pp. 332 and 339. For the resemblance of the microscopic character of the molar enamel of all Rodents (except Leporidae and Hystricidae) to that of the Proboscideans, see Trans. Odont. Soc. vol. iii. p. 239, 1871.
For the classiflcatory value of the ossicula auditus, see A. Doran, Tr. L. S. 1878, p. 418.
For other characters of the order Rodentia, see Waterhouse, Natural History of the Mammalia, vol. ii. pp. 1-9, 1848; De Quatrefages, Considerations sur les caracteres zoologiques des Rongeurs, Paris, 1840; Milne-Edwards, Recherches sur les Mammiferes, i. 1868, pp. 29, 30.
For those of the Myomorphi, see Osteological Catalogue, Royal College of Surgeons, vol. ii. Preparations 2223-2245; Waterhouse, Mag. Nat. Hist., l. c. p. 92; Brandt, /. c. pp. 152, 156, 300; Peters, Monatsber. Ak. Berlin, 1867.
For the Carpus and Tarsus and Shoulder-girdle, see Gegenbaur's Untersuch-ungen zur Vergleichenden Anatomie, Hft. i. ii. 1864, 1865; for the shoulder-girdle and sternum, see also Gotte, A. M. A. xiv. 1877; Ruge, M. J. vi. 1880; Hoffman, Niederland. Archiv fiir Zool. v. 1879-82. For the carpus, see Leboucq, Arch, de Biol. v. 1884; carpus and tarsus, Baur, Z. A. viii. 1885,
For the 'Canalis Temporalis,' or 'Foramen jugulare spurium,' see Otto, Nova Acta, xiii. pt. i. p. 27; Luschka, Dk. Wien. Akad. xx. 1862, p. 204; and Kolliker, Entwickelungsgeschichte, p. 929, 1879.
For the means whereby the vertebral centra are articulated in the different classes of vertebrata, see Rathke, Entwickelungsgeschichte der Wirbelthiere, mit einem Vorwort von A. Kolliker, 1861, p. 130.