THORACIC RESPIRATION 



307 



These ribs differ from the lower series in shape, articulation, 

 ligamentation, musculature and, consequently, in their move- 

 ments. 



(i) Shape. The upper ribs have a concave upper margin and 

 do not have such a marked twist as those in the lower costaJ 

 series. The second rib as a matter of fact may be laid flat on a 

 table. 



(ii) Articulation. The spinal articulation differs from the lower 

 series mainly in that the convex ovoid facet of the tubercle fits 

 into a corresponding cavity in the transverse process instead of 

 gliding on a flat facet. Each transverse 

 process from above downwards is tilted a 

 little more backwards so that the angle of 

 articulation becomes more oblique as one 

 passes down the series (Fig. 69). 



Further, the upper ribs not only articu- 

 late with the vertebral column by their 

 tubercles but also the facets on the head of 

 each rib work against the corresponding 

 facets on the head of the vertebra. 



(iii) Ligamentation. Each of the upper 

 series of ribs is joined directly to the sternum 

 by a band of cartilage. The following are 

 the lengths of these attachments in a well- 

 built man : second, 37 mm. ; third, 50 mm. ; 

 fourth, 62 mm. ; fifth, 75 mm. The angle 

 of attachment increases as the length in 

 creases, e.g. the second costal cartilage joins 

 the sternum at right angles while the third 

 ascends to the sternum. 



(iv) IduSCulatUTe The musculature of en ^ e ' n the obliquity of articu- 



these ribs is the intercostal interchondral. S" 1 the ex P ansion of the 



(v) Movements. Because of the double (From Noel Paton's Essent ials 

 .,. i-u j-u 4-Ui of Human Physiology.) 



articulation of each rib to the vertebral 



column by tubercle and head, rotation round a spino-sternal axis 

 is limited. Very little bucket-handle action can take place. As 

 the articulations are practically transverse, movement must occur 

 at the manubrio-sternal articulation, i.e. chiefly forwards. 



(c) The first rib provides the necessary fulcrum for the inter- 

 costal muscles. Along with the manubrium sterni, to which they 

 are firmly bound by their broad but short costal cartilages, the 

 first pair of ribs form the operculum or lid of the thorax. This 



FIG. 69. Bib and vertebral 

 column in upper and in lower 

 costal series to show the differ- 



