ELBOW. 77 



forearm. The flexor surface of the capsule is greatly 

 strengthened by more or less independent ligaments. 

 Garrod, Proc. Zool. Soc. 1875, p. 82. 



B. 142. Left elbow-joint of Duck-billed Platypus (Oriiitlw- 

 rhynchus anatinui). The humerus has been displaced to 

 show the form of the joint surfaces. The ulna lies directly 

 behind the radius, and their combined articular surfaces form 

 a simple concavity which plays upon a corresponding single 

 convex facet on the humerus. The joint forms a perfect 

 hinge. 



Tornier, Morph. Jahrb., Bd. xii. 1887, p. 407. 



B. 143. Right elbow-joint of a Koala (Phascolarctus einereus), 

 showing the form of the articular surfaces. The ulna lies 

 slightly to the inner side of the radius ; its articular surface 

 is composed of two distinct parts one of which, as in the 

 Monotremes, forms a simple concavity with that of the 

 radius and articulates with a single convex facet on the 

 humerus ; the other has the appearance of a lateral excres- 

 cence upon the inner side of the first and articulates with a 

 separate convexity on the head of the humerus. 



B. 144. A vertical section of the articular extremities of the 

 Human humerus and ulna, showing the trochlea of the 

 former bone to which the articular cavity of the latter is 

 adapted, and the mode in which the power of the triceps 

 brachii is increased by the projection of the olecranon, its 

 point of insertion, beyond the centre of motion. 0. C. 273. 



Hunterian. 



B. 145. Elbow-joint of Man dissected to show the form and 

 position of the orbicular ligament. 



The ligament is a strong fibrous band attached to the 

 anterior and posterior margins of the lesser sigmoid cavity ; 

 it encircles the head of the radius and is attached, proximally 

 to the capsular ligament, distally by a loose thin membrane 

 to the neck of the radius. It assists in pronation and 

 supination by allowing the radius to freely rotate upon its 

 own axis. 



Cathcart, Jour. Anat. & Physiol., vol. xix. 1885, p. 355. 



