i^ 



LECTURE III. 109 



The intervertebral connecting substance 

 is composed of concentric layers, of tough, 

 strong, and unyielding ligaments which 

 extend for about a quarter of an inch from 

 the circumference of the body towards its 

 centre, when the connecting substance ap- 

 pears softer, and is manifestly elastic; 

 which appearance continues till it ap- 

 proaches the centre, when the still con- 

 necting matter becomes pulpy and inelastic. 

 The exterior concentric layers of strong 

 unyielding ligament serve for security. 

 The quantity of elastic substance inter- 

 posed between the several vertebrae, is 

 not so great as to occasion any insecurity in 

 their connexion, yet the aggregate elasti- 

 city of the whole, renders the vertebral 

 column very springy; so that the head 

 rides upon its summit, undisturbed by jars, 

 and as upon a pliant spring. The central 

 inelastic matter admitting of a ready va- 

 riation of form, though not of bulk, serves 

 as a pivot facilitating the motion of the 

 vertebra on one another. Doctor Mac- 

 laurin in his lectures delivered more than 



