30 ATLAS AND TEXT-BOOK OF HUMAN ANATOMY. 



Fig. 21. — The vertebral column seen from in front (£). 

 Fig. 22. — The vertebral column seen from behind (£). 

 Fig. 23. — The vertebral column seen from the left side (J). 



of the sacral vertebras. The intervertebral foramina correspond to the similar structures in 

 the true vertebrae; but in the latter there are no openings comparable to the sacral foramina, 

 at least not in the bony spinal column. This is due to the fact that the spinal nerves divide into 

 an anterior and a posterior branch within the sacral canal instead of outside of the spinal canal 

 as in the true vertebrae, or, to go back a step further, it is due to the fact that whereas throughout 

 the series of true vertebrae the ribs or costal processes remain distinct from one another, in the 

 sacrum the costal processes, which are represented in the lateral masses, fuse together and also 

 unite with the transverse processes, so that the intervertebral canals are closed at their outer 

 ends. 



The apex of the sacrum presents an elliptical surface for articulation with the coccyx, and 

 at its sides there is a shallow notch which is converted into a foramen by the transverse process 

 of the first coccygeal vertebra and the connecting ligaments (see page 113). 



THE COCCYX. 



The coccyx (Figs. 18, 19, and 20) is a small bone of variable length formed by the fusion 

 of four or five (rarely three or six) quite rudimentary vertebrae (vertebra caudales). The first 

 vertebra alone shows some vertebral characteristics, since there can be recognized in it indica- 

 tions of transverse processes as well as of the upper articular processes which are transformed 

 into the coccygeal cornna. The transverse processes also frequently appear in the second ver- 

 tebra in the shape of feeble indistinct projections, but the remaining coccygeal vertebrae are 

 irregular, rounded pieces of bone. None of the coccygeal vertebrae possesses a trace of vertebral 

 arches or of a spinous process, and the individual vertebrae are united either by synchondroses 

 or (more rarely) by bony tissue. 



The sacrum shows typical sexual differences, since it is broader, shorter, and less curved in the female than in the 

 male. Not infrequently the first sacral vertebra remains partly or even entirely independent (the lumbosacral vertebra), 

 and the first coccygeal vertebra frequently fuses with the sacrum, in which case the sacral and coccygeal cornua are also 

 united by bony tissue. 



THE VERTEBRAL COLUMN AS A WHOLE. 



The vertebral column is completed by its ligamentous connections and particularly by the 

 intervertebral discs situated between the bodies of the vertebrae (see page no). If the bony 

 vertebral column be observed from the side (Fig. 23), its marked curvature at once becomes 

 apparent. This curvature is manifold, the cervical portion of the column being convex ante- 

 riorly, the thoracic portion markedly concave anteriorly, the lumbar portion decidedly convex 

 anteriorly, and the sacrum concave anteriorly. At the junction of the lumbar portion with 

 the sacrum, where the convexity of the former passes into the concavity of the latter there is 

 a marked angulation called the promontory. The curvatures of the vertebral column are sub- 

 ject to individual variation. 



