214 DETAILED SYNTHESIS. 



make them yield or to put them on the stretch. They 

 have a double elasticity, and equally tend to restore 

 themselves whether compressed or stretched, to lift the 

 Body up when bent forward, and to pull it up when 

 bent back, or to do both when it is bent to either side. 

 They, of course, grow tenaciously to the vertebrae above 

 and below them. 



315. THE BODIES OF THE VERTEBRAE AND THEIR 

 CARTILAGES FORM a tapering column of alternate thick 

 discs of resisting bone and thin discs of yielding elastic 

 cartilage, that, viewed in front or behind, should appear 

 straight, but to a side view should present the several 

 curves Fig. 1, PI. 12, which are owing to the varying 

 thicknesses of the back and front part of the bodies and 

 cartilages, and are necessary for giving proper form to 

 the cavities of the Trunk, carrying the head without jar 

 and flexing the column with ease. 



316. THE ARCHES OF THE VERTEBRJE are thin por- 

 tions of bone extending from the sides of the back part 

 of the bodies and arching around so as to enclose a 

 space, hole, or foramen, about as large as a thumb, so 

 that in the column there is a spinal canal back of the 

 bodies ; in this the spinal cord is located. 



317. A NOTCH EXISTS in each side of the arch close 

 by the body (see preceding Fig.). Through this notch 

 the corresponding nerve extends. 



318. THE ARTICULATING PROCESSES are small por- 

 tions of bone extending up and down from the arches 

 just back of the notches. The upper processes being 

 adapted to the lower ones of the vertebra above, a joint 

 is formed, that, in the preceding Fig., is represented as 

 surrounded by a capsular ligament, J, binding them to- 

 gether, yet allowing motion. It is lined by synovial 

 membrane, and a thin cartilage covers the surfaces of the 

 processes. It is called the spinal pivot-joint. 



815. What do ? Describe Fig. 8, PI. 12. 816. What are - ? 81T. Where does 

 >-? 818. What are ? Describe articulating processes, shown PI. 12. 



