PART THIRD. 



CHAPTEK I. 



THE TRUNK. 



PASSIVE ORGANS OF THE TRUNK. 

 THE BONES. 



Division. 1. Spine. 2. Thorax. 3. Pelvis. 



SECTION I. 



THE SPINE OR VERTEBRA. 



The spine, so called from its posterior projecting processes 

 resembling thorns, is situated on the posterior median line 

 of the trunk, and is composed of a column of bones, called 

 vertebral, placed one above the other in a regular series from 

 top to bottom, and designated the vertebral column. 



The vertebrae are divided into true and. false. The twenty- 

 four movable bones are the true ; the sacrum and coccyx, 

 which assist in forming the pelvis, the false. The true and 

 false vertebrae form an upright rod or column, having four 

 curvatures, one in the neck, concave behind and convex in 

 front ; a second in the back, concave in front and convex 

 behind ; a third in the loins, concave behind and convex in 

 front, and a fourth in the pelvis, concave in front and con- 

 vex behind. This arrangement is found to add greatly 

 to the strength of the spine, and results from the difference 

 in the thickness of the bodies of the several vertebrae, as 

 well as of the intervening fibro cartilage. 



The true vertebras are divided into cervical, dorsal, 

 and lumbar, as they are found in the neck, the back, or 

 the loins. The length of the true spine is estimated as 

 a general rule at twenty-four inches; six inches being 



