464 THE RIBS. 



by the middle costo-trans verse ligament. Its upper border 

 has a ridge for the attachment of the anterior or internal 

 cos to-transverse ligament. The tubercle is external to the 

 neck, and seen on the posterior under surface of the rib, 

 about an inch from the head. It consists of two portions, 

 an internal and external. The former is smooth, and articu- 

 lates with the transverse process, the latter gives attach- 

 ment to the external costo-iransverse ligament. On the out- 

 side of the tubercle the rib makes a turn which is called its 

 angle. To this the tendon of the sacro lumbalis muscle is 

 connected. This angle increases in distance from the tuber- 

 cle, from the first rib downward to the last, where it is not 

 so distinct. The anterior or sternal extremity is hollow 

 for the reception of the cartilage. Beyond or external to 

 the angle, is the body or shaft of the rib. Its external sur- 

 face is convex and smooth, and gives attachment to various 

 muscles. Its internal surface is concave and lined by the 

 pleura. Its superior margin is smooth and round, and gives 

 attachment to the intercostal muscles. The inferior is thin 

 and sharp, and has its inner side grooved, to lodge the in- 

 tercostal vessels and nerves, and for the attachment of the 

 intercostal muscles. 



Characters peculiar to some of the ribs. The first is the 

 shortest it is flat, strong and broad has its surfaces pre- 

 FIG. 139. senting upward and down- 



ward, instead of forward 

 and backward, has no angle 

 and is not twisted. Its head 

 has but one articular sur- 

 face, and is not divided. 

 There is no groove on the 

 inferior or rather posterior 

 edge. On the central part of the upper surface there is a 

 broad and shallow fossa for the subclavian artery. In front 

 of this is a slight eminence for the scale nus anticus muscle. 



Fio. 139 represents the upper surface of the first Rib. a Head. 6 Tuber- 

 cle, c Anterior surface, d Groove for subclavian artery. Groove for subcla- 

 vian vein. / Anterior extremity for cartilage, g Tubercle for scalenui anticus. 





