THE THORAX AS A WHOLE 83 



The first rib is the shortest, most curved, and the 

 broadest, the eighth the longest, after which they 

 decrease in length to the twelfth; the twelfth is the 

 narrowest. 



The Peculiar Ribs. The first rib is short, curved, 

 and not twisted. Its surfaces look upward and down- 

 ward. Head is small; neck is slender and rounded; 

 angle coincides with the tuberosity, which is strong 

 and placed on the outer margin of the rib. The upper 

 surface presents close in front of the tuberosity a 

 rough impression for the scalenus medius muscle, and 

 in front of the latter two smooth impressions with 

 an intervening ridge; the posterior impression lodges 

 the third portion of the subclavian artery, the ridge 

 affords attachment to the scalenus anticus muscle, and 

 the anterior impression receives the subclavian vein. 



The second rib is not twisted and has no angle; it 

 presents near its middle an impression for the scalenus 

 posticus muscle and two serrations of the serratus 

 magnus. 



The tenth rib has but one articular facet, usually. 

 The eleventh and twelfth ribs are short, have single 

 articular facets, and only slight elevations to mark 

 the tuberosities which do not articulate with the trans- 

 verse processes of the vertebra?. They are pointed 

 anteriorly. The eleventh has a slight subcostal groove; 

 the twelfth has no angle. 



There may be thirteen ribs. The twelfth rib measures 

 from 1 to 8 inches. 



The Costal Cartilages. These prolong the ribs to 

 the sternum and increase the elasticity of the thorax. 

 They consist of white hyaline cartilage. The first 

 seven pair connect the ribs and sternum, the next 

 three pair with the lower border of the cartilage of the 

 preceding rib. The cartilages of the last two ribs 

 (floating) have pointed extremities which terminate 

 in free ends. They increase in length from the first 

 to the seventh, then gradually diminish to the last. 



