CHAP. IV.] 



THE SKELETON. 



41 



A- 



by the union of the five sacral vertebrae, is a large triangular 

 bone situated like a wedge between 

 the ossa innominata ; it is curved 

 upon itself in such a way as to give 

 increased capacity to the pelvic 

 cavity (vide Fig. 47). The coccyx 

 is usually formed of four small seg- 

 ments of bone, and is the most 

 rudimentary part of the vertebral 

 column. 



The vertebral column as a whole. 

 The spinal column in a man of aver- 

 age height is about twenty-eight 

 inches long. Viewed from the side 

 it presents four curvatures; the first 

 curve has its convexity forwards in 

 the cervical region, and is followed 

 in the dorsal, by a curve with its 

 concavity towards the chest. In the 

 lumbar region the curve has again 

 its convexity forwards, while in the 

 sacral and coccygeal regions the con- 

 cavity is turned forwards. These 

 curvatures confer a considerable 

 amount of springiness and strength 

 upon the spinal column which would 

 be lacking were it a straight column: 

 the elasticity is further increased by 

 the disks of fibro-cartilage lying be- 

 tween and connecting the bodies of 

 the vertebrae. These di^ks or pads 

 also mitigate the effects of concussion 

 arising from falls or blows, and allow 

 of a certain amount of motion be- 

 tween the vertebrae. The amount 

 of motion permitted is greatest in 



the Cervical region. Between each vertebrae; 8 to 19, dorsal verte- 

 , , , , brae ; 20 to 24, lumbar vertebra ; 



pair of vertebrae are apertures through Af A> spinous processes; c, D, 



Which the Spinal nerves pass from transverse processes; E, inter- 

 vertebral aperture or foramen ; 



FIG. 41. SIDE VIEW OF SPI- 



the spinal cord. 



1, atlas; 2, axis. 



