ARTICULATIONS. 25 



adapts it so well for lubricating articular surfaces. Muscles and 

 tendons are discussed in Lecture VI. 



Kinds of motion are : flexion or bending, in which the two 

 articulating bones are brought nearer each other ; extension, the 

 reverse of flexion, by which bones are straightened on each other ; 

 adduction bringing the lower extremity of the moving bone to- 

 ward the median line; abduction in which the lower end of the 

 moving bone is carried from the median line; circumduction, in 

 which the articulation forms the apex of a cone circumscribed by 

 the moving bone; rotation in which one bone rotates as a pivot 

 on another. 



Joints are named according to the bones involved. In the 

 limbs the upper bone is named first. In the vertebrae, the an- 

 terior bone is named first. 



DESCRIBING ARTICULATIONS. 



Scapulo-humeral. — This is a ball and socket joint, the round- 

 ed head of the humerus fatting the glenoid cavity of the scapula. 



Ligaments at this joint are: (a) Glenoid, a cartilaginous 

 rim around the cavity which deepens the cavity; (b) capsular, 

 a sort of capsule fitting around the joint like a bag; (c) two 

 bundles of ligament fibers in front of the joint connecting the 

 extremities of the scapula and humerus. 



Movements. — All the motions, except true gliding, are pos- 

 sible at this articulation. The synovial membrane is quite loose 

 and affords a lining for the capsular ligament. 



First interphalangeal articulation. -This is an imperfect hinge 

 joint. The articular surface of the inferior extremity of the first 

 phalanx is characterized by two condyles and a median groove 

 which fit with two shallow cavities and a median ridge on the 

 superior extremity of the second phalanx. 



Ligaments. — The articular extremities which make up this 

 articulation are supported by the following ligaments and tendons : 

 in front by the tendon of the anterior extensor muscle; on the 

 sides by two lateral ligaments, one on each side; behind by the 

 posterior ligament and the tendons of the shallow and deep flexor 

 muscles which pass over the posterior of the joint. The pos- 

 terior ligament is really a thick strong pad of fibro-cartilage. 



Movements. — Flexion and extension, together with a limited 

 lateral movement. 



Vet. studies— 2. 



