42 HUMAN ANATOMY. 



dorsal vertebrae, separated by a ridge for the interarticular liga- 

 ment. 



The neck or constricted portion is smooth in front and 

 presents a rough surface behind for the middle costo-transverse 

 ligament, and a rough crest above for the anterior costo-trans- 

 verse ligament. 



The tubercle or tuberosity (wanting in eleventh and twelfth) 

 presents an articular surface for articulation with the transverse 

 process of the vertebra below, and a non-articular surface for 

 attachment of the posterior costo-transverse ligament. 



The shaft or body is flat, thin, and twisted on itself. Its 

 anterior extremity presents an oval depression for costal cartilage. 



The internal surface is smooth, concave, and presents in 

 front of the angle a ridge, forming the side of the groove on the 

 inferior border. 



The external surface is rough, convex, and presents a little 

 in front of the tubercle a bend or angle marked by a prominent 

 line, and near the sternal extremity another bend, the anterior 

 angle, marked by an oblique line. 



The superior border is round and thick, and presents an 

 external and internal lip for external and internal intercostal 

 muscles. 



The inferior border at its posterior third presents a groove 

 for the intercostal vessels and nerve, and at its anterior two- 

 thirds is sharp and thin. 



Peculiar Ribs. The peculiar ribs are the first, second, tenth, 

 eleventh, and twelfth. 



The first is short, broad, and has no angle, and but one 

 facet on the head. Its upper surface is marked by two parallel 

 grooves, the anterior for the subclavian vein, the posterior for 

 the artery, separated by a tubercle for insertion of scalenus an- 

 ticus muscle, an important guide in ligation of the subclavian 

 artery. 



The second resembles the first in being flattened and not 

 twisted. The tubercle and angle are slight and almost coincide 

 in position. The outer surface of the shaft presents near its 

 middle a rough eminence for the second and third portions of the 

 serratus magnus. 



The tenth rib has but one facet for articulation with the 

 tenth dorsal vertebra. 



The eleventh has single facet on head, slight angle, but no 

 tubercle or neck. 



The twelfth, single facet, but no angle, tubercle, or neck. 



The ribs articulate with twelve vertebra? behind and twelve 

 costal cartilages in front. 



