THE PRIXCIPLES OF MYO DYNAMICS. 



79 



ward about 1 30 degrees : Flexion and extension. 



{3.) In earl)' life the fore-arm moves outward 

 and inward, sometimes as much as i5 degrees : 

 Abdnction and adduction. — a lateral ginglymus. 



66. The elbow joint has two essential parts : 



A. (1.) The ulno-numeral articulation is a 

 hinge -joint, and the greater sigmoid cavity of 

 the ulna always embraces the trochlea of the 

 humerus. 



(2.) The radio-humeral articulation is a hinge- 

 joint and a ball -and- socket -joint, having a shallow 

 socket in the head of the movable bone, and a 

 small head on the fixed bone. The radius has 

 only scnii-circiundnction. which, in so far as the 

 ulna is concerned, is rotation. 



B. (i.) The distal end of the humerus, from 

 the grove of the trochlea outward, is nearly 

 transverse to the long axis of the humerus. 



(2.) The lip of the trochlea projects down- 

 ward about 30 degrees from the transverse di- 

 ameter of the condyles of the humerus. This lip 

 antagonizes the inward lateral displacing com- 

 ponents of such muscles as are attached to the 

 internal condyle, and run obliquely downward 



