destitute of a central ridge or keel, and the wings are minute and quite rudimentary; so that Hesperornis. unlike Ichthyornis, Fig. 324-Toothed Birds (Odontornithes) of the Cretaceous rocks of America. a. Left lower jaw of Ichthyornis dispar, slightly enlarged; b, Left lower jaw of Hesper TEJ regalis, reduced to nearly one-fourth of the natural size: c, Cervical vertebra of Ichthyornis dispar, front view, twice the natural size; c', Side view of the same; d Tooth of Hesperornis regalis, enlarged to twice the natural size. (After Marsh.) must have been wholly deprived of the power of flight, in this respect approaching the existing Penguins. The tail consists of about twelve vertebræ, of which the last three or four are amalgamated to form a flat terminal mass, there being at the same time clear indications that the tail was capable of up and down movement in a vertical plane, this probably fitting it to serve as a swimming-paddle or rudder. The vertebræ of the cervical and dorsal regions are of the ordinary ornithic type. The legs were powerfully constructed, and the feet were adapted to assist the bird in rapid motion through the water. The known remains of Hesperornis regalis prove it to have been a swimming and diving bird, of larger dimensions than any of the aquatic members of the class of Birds with which we are acquainted at the present day. It appears to have stood between five and six feet high, and its inability to fly is fully compensated for by the numerous adaptations of its structure to a watery life. Its teeth prove it to have been carnivorous in its habits, and it probably lived upon fishes. From the next order, the present is readily distinguished by the fact that the vertebra resemble those of recent birds, the ster num is without a keel, the wings are rudimentary, and the teeth are implanted in a groove in the jaw and not in separate sockets. ORDER II. ODONTOTORMÆ.-This order has been founded by Marsh for the reception of two remarkable birds, which he has named Ichthyornis dispar and Apatornis celer, both from the Cretaceous rocks of North America. In Ichthyornis dispar, which may be taken as the type of the order, the teeth (fig. 324, a) were sunk in distinct sockets, and were "small, compressed, and pointed, and all of those preserved are similar. Those in the lower jaw number about twenty in each ramus, and are all more or less inclined backwards. . . The maxillary teeth appear to have been equally numerous, and essentially the same as those in the mandible. The skull was of moderate size, and the eyes placed well forward. The lower jaws are long and slender, and the rami were not closely united at the symphysis. The jaws were apparently not encased in a horny sheath. "The scapular arch, and the bones of the wings and legs, all conform closely to the true ornithic type. The wings were large in proportion to the legs, and the humerus had an extended radial crest. The metacarpals were united, as in ordinary birds. The bones of the posterior extremities resemble those of swimming birds. The vertebræ (see fig. 324, c and c) were all biconcave, the concavities at each end of the centra being distinct and nearly alike. Whether the tail was elongated cannot at present be determined; but the last vertebra of the sacrum was unusually large. "The bird was fully adult, and about as large as a pigeon. With the exception of the skull, the bones do not appear to have been pneumatic, though most of them are hollow. The species was carnivorous, and probably aquatic." (Marsh.) Apatornis agrees with Ichthyornis in most of the above characters, but the structure of its jaws is not fully known. It follows from the above that the order Odontotorma is characterised by the possession of distinct teeth sunk in separate sockets in the jaw and not in a continuous groove, by the fact that the vertebra are biconcave, and by the possession of a carinate sternum and well-developed wings. LITERATURE. [In addition to many of the works mentioned in the list of treatises relating to the Vertebrata in general, the following are some of the more important sources of information as to recent and fossil Birds : :-) 1. Article "Aves." Owen. 'Todd's Cyclopædia of Anat. and Phys.' 1836. 2. Article "Birds." Newton and Parker. Encyclopædia Britannica.' 9th edt. 1875. 3. "Genera of Birds." G. R. Gray. 1844-49. 66 4. System der Pterylographie.' Nitzsch and H. Burmeister. 5. "Pterylography." Nitzsch. 1867. 1840. Translated by Sclater. Ray. Soc.' 6. "Manuel d'Ornithologie." Temminck. 1820. 7. "Natural History and Classification of Birds." Swainson. 1836. 8. "On the Classification and Distribution of the Alectoromorpha and Heteromorpha." Huxley. Proc. Zool. Soc.' 1868. 9. IO. II. 12. 13. "On the Classification of Birds." Huxley. 'Proc. Zool. Soc.' 1867. "Aves." Selenka. 'Bronn's Klassen und Ordnungen des Thierreichs.' 1869. "Elements of Embryology." Foster and Balfour. 1874. "On the Osteology of Gallinaceous Birds and Tinamous." Parker. 'Trans. Zool. Soc.' 1866. 66 "On the Skull of the Ostrich." Parker. 'Phil. Trans.' 1866. 14. Essai sur l'appareil locomoteur des Oiseaux." Alix. 1874. 15. "Animal Locomotion." Pettigrew. 1873. 16. "Recherches Anatomiques et Paléontologiques pour servir à l'histoire des Oiseaux fossiles de la France." Alphonse Milne-Edwards. 1867-77. 17. 18. "British Fossil Mammals and Birds." Owen. 1846. 66 1842. 19. Anatomy of the Southern Apteryx." Owen. 'Trans. Zool. Soc.' 20. 21. 22. 23. 1838 and 1842. "On Dinornis." Owen. Trans. Zool. Soc.' 1839-64. Osteology of the Dodo.' Owen. 'Trans. Zool. Soc.' 1867. "The Dodo and its kindred." Strickland and Melville. 24. Archeopteryx macrura." Owen. 'Phil. Trans.' 1863. 25. "On the Odontornithes or Birds with Teeth." Marsh. 66 Magazine.' 1876. 26. "Geographical Distribution of Animals." Wallace. 1876. "General History of Birds." Latham. 1821-28. 27. 'Geol. 28. "Anatomie und Naturgeschichte der Vögel." Tiedemann. 1810-14 29. "Histoire Naturelle, générale et particulière, des Oiseaux." 31. Buffon. An. xiv. (Eng. Translation by Smellie. 1793-) History of British Birds." Bewick. 6th ed. 1826. 30. 66 History of British Birds." 66 32. History of British Birds." Macgillivray. 1839-41. Yarrell. 33. 1874, 1875, 1877. Bowdler Sharpe. 34. 35. 36. 37. 38. 39. 40. Monograph of the Trochilidæ." Gould. Monograph of the Rhamphastida.' Gould. 1833-35. Monograph of the Alcedinidæ." Sharpe. 1871. Iconographie Ornithologique." Audubon. 43. "Birds of America." Audubon. Des Murs. 1849. 1826. (Abridged from the larger work.) American Ornithology." Wilson. 1808-14. Catalogue of North American Birds." Baird. 1859. 46. "Key to North American Birds." Coues. 1872. 47. "Fauna Boreali Americana." Richardson. (The Birds by Swainson.) 1831. 48. "Distribution and Migration of American Birds." Baird. 'Amer. Journ. Sci. and Arts.' 1866. 49. "Manual of the Ornithology of the United States and Canada." Nuttall. 2d ed. 1840. 614 DIVISION III-MAMMALIA. CHAPTER LXIX. GENERAL CHARACTERS OF THE MAMMALIA. THE last and highest class of the Vertebrata, that of the Mammalia, may be shortly defined as including Vertebrate animals in which some part or other of the integument is always provided with hairs at some time of life; and the young are nourished, for a longer or shorter time, by means of a special fluid—the milk— secreted by special glands-the mammary glands. These two characters are of themselves sufficient broadly to separate the Mammals from all other classes of the Vertebrate sub-kingdom. In addition, however, to these two leading peculiarities, the Mammals exhibit the following other characters of scarcely less importance: 1. The skull articulates with the vertebral column by means of a double articulation, the occipital bone carrying two condyles, in place of the single condyle of the Reptiles and Birds. 2. The lower jaw or mandible consists of two halves or rami, united anteriorly by a symphysis, but not necessarily anchylosed; but these are each composed of a single piece, instead of being complex and consisting of several pieces, as in the Reptiles and Birds. Further, the lower jaw always articulates directly with the squamosal element of the skull, and is never united to an os quadratum, as in the Sauropsida. 3. The two hemispheres of the cerebral mass, or brain proper, are united together by a more or less extensively developed corpus callosum" or commissure. 66 4. The heart consists-as in Birds-of four cavities or chambers, two auricles and two ventricles. The right and left sides of the heart are completely separated from one another, and there is no communication between the pulmonary and systemic circulations. The red blood - corpuscles are nonnucleated, and, with the exception of those of the Camelida, |