SYSTEMATig SYNTHESIS OF TISSUES INTO ORGANS. 213 



skull, binding both atlas and dentatus to the skull, 

 yet allowing sufficient motion to each (see Fig. 5, 4, 

 PI. 16). 



310. THE USE OF THE DENTATUS is to allow a rotary 

 motion to the head, as in negation. 



311. THE TWENTY-TWO LOWER VERTEBRAE are very 

 similar to each other in all general respects, increasing 

 in size and thickness from top to bottom (see PI. 12, 

 13). They are composed of body, arches, and seven pro- 

 cesses. 



312. THE BODIES OF THE VERTEBRJE are cylindrical 

 blocks of bone, slightly flattened, or even concave, on 

 the back, not very dense at the surface, and spongifonn 

 within. 



313. INTERVERTEBRAL SUBSTANCES situated between 

 the vertebra?, as represented in the figures, are fibro-car- 

 tilages, having but few cells, the fibres woven very 

 densely at and near the margin, but not as closely to- 

 ward and in the centre, the minute meshes being filled 

 with serous moisture and chondrine. 



FIG. 163. 



Fig. 163 represents 

 a section of one and 

 part of another verte- 

 bra with the interven- 

 ing cartilage, of which 

 1 represents the fibres 

 curving outward, 2, 

 curving inward, and 

 3, the more yielding 

 centre, containing car- 

 tilage cells. It is, 

 therefore, both liga- 

 ment and cartilage. 



314. THE ELASTICITY OF THE INTERVERTEBRAL SUB- 

 STANCES is their interesting and useful characteristic. 

 They possess a much greater degree of firmness than 

 India rubber, and considerable pressure is required to 



310. What ? 811. What said of ? 812. What said of ? 81& What said of -? 

 Describe Fig. 163. 314. What said of ? 



