FUNCTIONS OF LOCOMOTION. 71 



joined by an intermediate fibrous and elastic tissue, which 

 allows a certain amount of motion. The short bones are 

 articulated together in this manner. 



In the mobile articulation the extremities of the bones 

 that come together are free ; they touch by surfaces re- 

 ciprocally concave and convex, each being covered by a 



FIG. 39. 



BONES OF THE HEAD. 1, frontal bone; 2, parietal bone; 3, temporal bone; 

 4, occipital bone ; 5, nasal bone ; 6, malar bone ; 7, upper jaw ; 8, os unguis ; 

 9, lower jaw (maxilla). 



cartilaginous pad. This pad facilitates the gliding of the 

 surfaces one on the other, and the friction is still further 

 diminished by a viscous liquid, called synovial fluid, se- 

 creted by synovial capsules, membranes that surround 

 all mobile articulations. Strong fibrous cords, called lig- 

 aments, are attached to the extremities of both articu- 

 lating bones, and hold the ends in position. Motion is 



