196 



THE MECHANISM OF 



THE FIRST RIB, MANUBRIO-STERNAL JOINT, AND THEIR 

 RESPIRATORY SIGNIFICANCE 



The first rib has always been treated as merely one of the 

 costal series. Its articulation to the spine, its ligaments, its 

 muscles, its shape, its costal cartilage, its intimate union with 

 the manubrium sterni, differ so markedly from the corresponding 

 features of other ribs, that were only the anatomical evidence avail- 

 able, one would conclude that it differed from all the others in 

 its respiratory function. An examination of its movements and 

 of the part it plays in expanding the lung shows this is so. The 

 first pair of ribs and the manubrium sterni are bound intimately 



VII. Cerv. Vert. 

 Neck of I 



FIG. 2. Diagram to show the respiratory movements of the first pair of ribs and 

 nianubrium sterni, and the effect of these movements on the expansion of the apex 

 of the lung. 



together by the broad and short first pair of costal cartilages, 

 and form with the manubrium, a united structure which may be 

 described as the lid or operculum of the thorax. Behind, this 

 lid is articulated to the spinal column by a joint which is set more 

 transversely and is wider in the extent of its attachment than 

 any other of the costal arcs ; in front the lid is articulated with 

 the body of the sternum at the manubrio-sternal joint. The 

 manubrio-sternal joint must be counted amongst the important 

 respiratory joints. Anchylosis of this joint is rarely seen before 

 the fiftieth year, and it is uncommon before the sixtieth. The 

 respiratory movement which occurs at it varies with the indi- 

 vidual, with the type of respiration, being greatest in those with 



