(The same figures indicate the corresponding parts in each).

1. Skull.

2. Atlas.

3. Dentata.

4-8. Cervical vertebrae. 9-27. Dorsal vertebrae. 28-33. Lumbar vertebras. 34-38. Sacral vertebrae. 39-52. Coccygeal vertebras.

53. Ribs.

54. Sternum.

55. Scapula. 56: Humerus.

57. Elbow-joint.

58. Olecranon.

59. Ulna.

60. Radius.

61. Pisiform bone.

62. Lunar bone.

63. Cuneiform bone. lit. Os magnum.

65. Unciform bone.

a. Carpus.

66. Small metacarpal.

67. Large metacarpal.

b. Metacarpus.

68. Sesamoid bone.

69. Fetlock-joint.

70. Os suffraginis.

71. Os coronae.

72. Os pedis or pedal bone.

c. Phalanges.

73. Navicular bone.

74. Innominatum.

75. Tuberosity of ischium.

76. Hip-joint.

77. Femur.

78. Patella.

79. Stifle-joint (true knee).

80. Fibula.

81. Tibia.

82. Os calcis (true heel).

S3. Astragalus.

84. Cuboid.

85. Os magnum.

86. Os medium.

87. Os parvum.

d. Tarsus.

88. Large metatarsal.

89. Small metatarsal.

e. Metatarsus.

90. Os suffraginis.

91. Os coronae.

92. Os pedis or pedal bone.

■f. Phalanges.

PLATE XXXVII. SKELETONS OF HORSE AND MAN.

By permission, from the Mounted Skeletons in the Natural History Museum, South Kensington.

If a very thin transverse section of bone (fig. 281) be made, and subjected to the scrutiny of the microscope, it will be found to present a definite order of arrangement of its several parts, conspicuous among which are a number of openings 1/2500 to 1/200 inch in diameter. These are the Haversian canals, so called from the name of the person (Havers) who first detected them. The Haversian canals are each surrounded by a group of bony rings arranged concentrically or one outside another. In and between these rings will be noticed a number of small spider-like bodies (lacunae) from which fine dark lines (canaliculi) radiate in all directions. If a similar section be made longitudinally, and inspected under a similar power, what in the first appeared as openings will now come into view as tubes traversing the bone tissue (fig. 282), and dividing and reuniting; the same dark lacunae and canaliculi intervening between them.

The Haversian canals are so many channels for the accommodation of blood-vessels, by which the circulation in the bone is carried on.

The lacunae are small corpuscles or spaces containing a mass of living protoplasm, and the fine lines proceeding from them are minute channels which communicate with each other and with the Haversian canals, into which some of them open. These channels serve the purpose of distributing nutritive matters for the support of the bone tissue.