54 



THE H0K8E IN HEALTH AND DISEASE 



relation, and uses. Each muscle has at least two attachments, 

 known as origin and insertion. The origin is the point which usu- 

 ally remains fixed while the muscle contracts. The insertion or 

 termination is the point which is fixed to the bone that is displaced 

 by the muscular contraction. This is not a hard-and-fast rule, 

 for the action may lie reversed and the insertion Ijecome the 

 origin, as is the case when the heatl and neck are inclined to one 

 side b}' the contraction of the niastoido-humeralis. Muscles are 

 arranged in groups that oppose each other when they act on the 



Fig. 9. — Cross-section of left leg, cut a little above middle: u, Tibia; h, 

 fibula; d, I, m, tendons of muscles; c, e,f, g, h, i, k, ti, fleshy portions of muscles; 

 o, skin; p, s, iv, arteries; r, x, veins; q, <j', r, I, ii, ij, nerves. (EUenberger in 

 Leisering's Atlas.) 



joints, one group acting as flexors and the antagonistic group as 

 extensors. 



To facilitate the play of a muscle or tendon over bony promi- 

 nences are liursse and tendon sheaths. Bursas are small sacs filled 

 with a fluid which resembles synovia. They form pads to prevent 

 friction. The tendon sheaths are elongated, closed sacs containing 

 serous fluid. They are folded completely around the tendons, as 

 the diagram (Fig. 10) shows. 



Each skeletal muscle has a name. Names of muscles have 



