I 



STERNOCLAVICULAR ARTICULATION 313 



shape and that of the interlocking mechanism on its surfaces; a rotatory movement, however, 

 is produced by which the anterior segment is tilted downward and the posterior upward; the axis 

 of this rotation passes through the dorsal part of the middle segment. The movement of the 

 anterior segment is slightly limited by its wedge form, but chiefly by the posterior and inter- 

 osseous sacroiliac ligaments; that of the posterior segment is checked to a, slight extent by its 

 wedge form, but the chief limiting factors are the sacrotuberous and sacrospinous ligaments. 

 In all these movements the effect of the sacroiliac and iliolumbar ligaments and the ligaments 

 of the symphysis pubis in resisting the separation of the iliac bones must be recognized. 



During pregnancy the pelvic joints and ligaments are relaxed, and capable therefore of more 

 extensive movements. When the fetus is being expelled the force is applied to the front of the 

 sacrum. Upward dislocation is again prevented by the interlocking mechanism of the middle 

 segment. As the fetal head passes the anterior segment the latter is carried upward, enlarging 

 the antero-posterior diameter of the pelvic inlet; when the head reaches the posterior segment 

 this also is pressed upward against the resistance of its wedge, the movement only being possible 

 by the laxity of the joints and the stretching of the sacrotuberous and sacrospinous ligaments. 



ARTICULATIONS OF THE UPPER EXTREMITY. 



The articulations of the Upper Extremity may be arranged as follows: 



I. Sternoclavicular. VI. Wrist. 



II. Acromioclavicular. VII. Intercarpal. 



III. Shoulder. VIII. Carpometacarpal. 



IV. Elbow. IX. Intermetacarpal. 



V. Radioulnar. X. Metacarpophalangeal. 



XI. Articulations of the Digits. 



I. Sternoclavicular Articulation (Articulatio Sternoclavicularis) (Fig. 325). 



The Sternoclavicular articulation is a double arthrodial joint. The parts entering 

 into its formation are the sternal end of the clavicle, the upper and lateral part 

 of the manubrium sterni, and the cartilage of the first rib. The articular surface 

 of the clavicle is much larger than that of the sternum, and is invested with a layer 

 of cartilage, 1 which is considerably thicker than that on the latter bone. The 

 ligaments of this joint are: 



The Articular Capsule. The Interclavicular. 



The Anterior Sternoclavicular. The Costoclavicular. 



The Posterior Sternoclavicular. The Articular Disk. 



The Articular Capsule (capsula articularis; capsular ligament}. The articular 

 capsule surrounds the articulation and varies in thickness and strength. In front 

 and behind it is of considerable thickness, and forms the anterior and posterior 

 Sternoclavicular ligaments; but above, and especially below, it is thin and par- 

 takes more of the character of areolar than of true fibrous tissue. 



The Anterior Sternoclavicular Ligament (ligamentum sternoclaviculare anterior). 

 The anterior Sternoclavicular ligament is a broad band of fibers, covering the 

 anterior surface of the articulation; it is attached above to the upper and front part 

 of the sternal end of the clavicle, and, passing obliquely downward and medialward, 

 is attached below to the front of the upper part of the manubrium sterni. This 

 ligament is covered by the sternal portion of the Sternocleidomastoideus and the 

 integument; behind, it is in relation with the capsule, the articular disk, and the 

 two sy no vial membranes. 



The Posterior Sternoclavicular Ligament (ligamentum sternoclaviculare postering. 

 The posterior Sternoclavicular ligament is a similar band of fibers, covering the 

 posterior surface of the articulation; it is attached above to the upper and back 



1 According t.o Bruch, the sternal end of the clavicle is covered by a tissue which is fibrous rather than cartilaginous 

 in structure. 



