21(5 THE ARTICULATIONS 



where the bulkiest part of the hing is enclosed. This is (jn a level with the sixth, 

 seventh, and eighth rihs. 



At the lower part of the thorax, where the ribs have no relation to the lungs, and 

 do not affect respiration directly V)y their movements, it is important that the costal 

 arches should l)e thrown well outwards in order to counteract the compression of 

 the abdominal viscera l)y the contraction of the diaphragm. 



By widening and steadying the lower part of the thorax during inspiration, the 

 attachments of the muscular fibres of the diaphragm are widened, and their power 

 increased. 



THE ARTICULATIONS OF THE UPPER EXTREMITY 



The articulations of the upper extremity are the following: — 



1. The sterno-costo-clavicular. 



2. The scapulo-clavicular union. 



3. The shoulder-joint. 



4. The elbow-joint. 



5. The radio-ulnar union. 



6. The radio-carpal or wrist-joint. 



7. The carpal joints. 



8. The carpo-metacarpal joints. 



9. The intermetacarpal joints. 



10. The metacarpo-phalangeal joints. 



11. The interphalangeal joints. 



1. THE STERNO-COSTO-CLAVICULAR ARTICULATION 



Class. — I) I arthrosis. Subdivision. — Sad die- shaped Arthrodia. 



At this joint the large iimer end of the clavicle is united to the superior angle 

 of the manubrium sterni, the first costal cartilage also assisting to support the 

 clavicle. It is the only joint between the up})er extremity and the trunk, and takes 

 part in all the movements of the upper lind). Looking at the bones, one wouhl 

 say that they were in no way adapted to articulate with one another, and yet the}' 

 assist in constructing a joint of great security, strength, and importance. The 

 bones are nowhere in actual contact, being completely separated by an inter- 

 articular cartilage. The interval Ix'tween the joints of the two sides varies from 

 one inch to an inch and a half (2-5-4 cm.). The ligaments of this joint are: — 



(1) Capsular. (3) Interarticular fibro-cartilage. 



(2) Interclavicular. (4) Rhoml)oid or costo-clavicular. 



The capsular ligament (figs. 219 and 220) consists of fibres, having varying 

 directions and l)cing of various strength and thickness, which comi)letely surround 

 the articulation, and are firndy connected with the edges of the interarticular fil)ro- 

 cartilage. The fibres at the back of the joint, sonietimes styled the posterior 

 sterno-clavicular ligament, are stronger than those in front or below, and consist 

 of two sets: a su])crficial, passing upwards and outwards from the manubrium 

 sterni, to the i)rojccting jjosterior edge of the inner end of the clavicle, a few 

 being prolonged onwards ui)on the i)osterior surface of the bone. A deeper set of 

 fibres, especially thick and numerous below the clavicle, connect the interarticular 

 cartilage with the clavicle and with the sternum, but do not extend from one lione 



