74. From the posterior surface of the column, which is every where irregular and rough, spring, along the median line, in regular series, strong, sharp, and pointed projections of bone (fig. XXXV.), which from being sharp and pointed, like elongated spines, are called spinous processes, and have given name to the whole chain of bones. These processes afford fixed points for the action of powerful muscles. Extending the whole length of the column, from the base of the skull to the sacrum, on each side of the spinous processes, are deep excavations, which are filled up with the powerful muscles that maintain the trunk of the body erect.
75. From the lateral surfaces of the column likewise spring short but strong projections of bone, termed transverse processes, which also give attachment to powerful muscles (fig. XLVI.).
Bones of the trunk. 1. Spinal column; 2. the seven cervical
vertebræ; 3. the twelve dorsal vertebræ; 4. the five
lumbar vertebræ; 5. the sacrum; 6. the sternum; 7. the
true ribs; 8. the false ribs; 9. the clavicle; 10. the scapula;
11. the ilium; 12. the ischium; 13. the pubes;
14. the acetabulum; 15. the brim of the pelvis.
76. The separate bones of the series have a kind of turning motion on each other; hence each is called a vertebra, and the name of vertebral column is often given to the entire series, as well as that of spinal column. That portion of the column which forms the neck consists of seven distinct bones, called cervical vertebræ (fig. XLV. 2); that portion which forms the back consists of twelve, called dorsal vertebræ (fig. XLV. 3); that portion which forms the loins consists of five, called lumbar vertebræ (fig. XLV. 4). Between each of these classes of vertebræ there are specific differences, but they need not be described here: all that is necessary to the present purpose is an account of the structure which is common to every vertebra.
77. By inspecting fig. XLVI. 1, it will be seen that the upper and under edges of each vertebra consist of a ring of bone, of a firm and compact texture, rendering what may be called the body of the vertebra exceedingly strong (fig. XLVI. 3). This ring of bone forms a superficial depression (fig. XLVI. 2), for the reception of a peculiar substance, immediately to be described, which is interposed between each vertebra (fig. XLVII. 2).
78. The anterior surface of the body of the vertebra is convex (fig. XLVI. 3); its posterior surface is concave (fig. XLVI. 4); from the posterior surface springs a bony arch (figs. XLVI. 5 and LIII. 1), which, together with the posterior concavity, forms an aperture of considerable magnitude (fig. XLVI. 6), a portion of the canal for the passage of the spinal cord (figs. XLVII. 3, and XLIX. 3).
