248 THE ARTICULATIONS 



muscles also come into plaj-: The pectoralis minor, the muscles which extend the head and the 

 cervical part of the vertebral column, the sterno-mastoid and the supra- and infra-hyoid mus- 

 cles, the lower fibres of the pectoralis major, some of the lower fibres of the serratus anterior, and, 

 when the clavicle is fixed, the subclavius. , • ■, , 



Expiration is produced by the elasticity of the lungs and the weight of the thorax, aided 

 by the elastic reaction and contraction of the external and internal obhque muscles, the recti 

 and pyramidales, the transversus abdominis, and the levatores ani and coccygei. In forcible 

 expiration all muscles which depress the ribs and reduce the dimensions of the abdomen are 

 thrown into action. The internal intercostals probably tend to contract the thorax, excepting, 

 the parts between the costal cartilages, which tend to expand the thorax. 



THE ARTICULATIONS OF THE UPPER EXTREMITY 



The articulations of the upper extremity are the following :— 



1. The stemo-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. — Diarthrosis. Subdivision. — Condylarthrosis. 



At this joint the large medial 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 upper extremity and the trunk, and 

 takes part in all the movements of the upper limb. Looking at the bones, one 

 would say that they were in no way adapted to articulate with one another, and 

 3'et they assist in constructing a joint of security, strength, and importance. 

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

 articular disc. The interval between 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) Articular capsule. (3) Articular disc. 



(2) Interclavicular. (4) Costo-clavicular. 



The articular capsule (fig. 284) consists of fibres, having varying directions 

 and l)eing of various strength and thickness, which completely surround the 

 articulation, and are firmly connected with the edges of the interarticular fibro- 

 cartilage. 



The fibres at the back of the joint, sometimes styled the posterior stemo- clavicular liga- 

 ment, are stronger than those in front or below, and consist of two sets: a superficial, passing 

 upward and laterally from the manubrium sterni, to the projecting posterior edge of the end of 

 the clavicle, a few being prolonged onward upon the posterior surface of the bone. A deeper 

 sot of fil)re3, especially thick and numerous below the clavicle, connect the interarticular car- 

 tilage with the clavicle and with the sternum, but do not extend from one bone to the other. 

 The fil^res in front, the anterior sterno-clavicular ligament, are well marked, but more lax and 

 le.sH tough than the j)ostcrior, and are overlaid by the tendinous sternal origin of the stcrno- 

 matitfdd, the fibres of which run parallel to those of the ligament. They extend obliquely up- 

 ward and laterally from the margin of the sternal facet to the anterior surface of the clavicle 

 some little distance from the articular margin. The fibres which cover in the joint below are 

 short, woolly, and consi.st more of fil)ro-arcolar tissue than true fibrous tissue; they extend from 

 the u[)per border of the first (to.stal cartilage to the lower border of the clavicle just lateral to 

 the articular margin, aiul fill up the gaj) between it and the costo-clavicular ligament. The 

 superior portion consi.st h of .short tough fibres i)assing from the sternum to the articular disc; 

 and r)f others weldir)g the fibro-cartilage to the upper edge of the clavicle, only a few of them 

 passing from the clavicle direct to the sternum. 



The interclavicular ligament (fig. 284) is a strong, concave band, materially 

 strengthening the superior portion of the capsule. It is nearly a quarter of an 



