CHAP. IV.] THE SKELETON OF THE LIMBS. 123 



can rotate. It resembles in principle tlie joint last noticed, but here 

 the part bearing the ring (which ring is formed partly of bone, partly 

 of ligament) itself turns on the bone, which traverses it instead of the 

 reverse. 



Certain ligaments are called elastic ligaments, because they contain 

 clastic tissue, and so serve to sustain weight, and overcome persistent 

 resistance, without the necessity of expending any muscular power. 

 Such are the ligaments between the neural arches of the vertebras 

 and their continuation onwards to the occiput (to support the head), 

 as the ligament um nuchce. 



