74 RIBS. TRUE AND FALSE. 



and two extremities ; it is curved to correspond with the arch of the 

 thorax, and twisted upon itself, so that, when laid on its side, one 

 end is tilted up, while the other rests upon the surface. 



The external surface is convex, and marked by the attachment of 

 muscles ; the internal is flat, and corresponds with the pleura ; the 

 superior border is rounded ; and the inferior sharp and grooved upon 

 its inner side, for the attachment of the intercostal muscles.* Near its 

 vertebral extremity, the rib is suddenly bent upon itself; and opposite 

 the bend, upon the external surface, is a rough oblique ridge, which 

 gives attachment to a tendon of the sacro-lumbalis muscle, and is 

 called the angle. The distance between the vertebral extremity and 

 the angle increases gradually, from the second to the eleventh rib. 

 Beyond the angle is a rough elevation, the tubercle; and immediately 

 at the base and under side of the tubercle a smooth surface for 

 articulation with the extremity of the transverse process of the corre- 

 sponding vertebra. The vertebral end of the rib is somewhat ex- 

 panded, and is termed the head, and that portion between the head 

 and the tubercle is the neck. On the extremity of the head is an 

 oval smooth surface divided by a transeverse ridge into two facets 

 for articulation with two contiguous vertebrae. The posterior sur- 

 face of the neck is rough, for the attachment of the middle costo- 

 transverse ligament ; and upon its upper border is a crest, which gives 

 attachment to the anterior costo-transverse ligament. The sternal 

 extremity is flattened, and presents an oval depression, into which the 

 costal cartilage is received. 



The ribs that demand especial consideration are the first, tenth, 

 eleventh, and twelfth. 



The first is the shortest rib ; it is broad and flat, and placed horizon- 

 tally at the upper part of the thorax, the surfaces looking upwards and 

 downwards, in place of forwards and backwards as in the other ribs. 

 At about the anterior third of the upper surface of the bone, and near 

 its internal border, is a tubercle which gives attachment to the scalenus 

 anticus muscle, and immediately before and behind this tubercle, a 

 shallow oblique groove, the former for the subclavian vein, and the 

 latter for the subclavian artery. Near the posterior extremity of the 

 bone is a thick and prominent tubercle, with a smooth articular sur- 

 face for the transverse process of the first dorsal vertebra. There is no 

 angle. Beyond the tuberosity is a narrow constricted neck ; and at 

 the extremity, a head, presenting a single articular surface. The 

 second rib approaches in some of its characters to the first. 



The tenth rib has a single articular surface on its head. 



The eleventh and twelfth have each a single articular surface on the 

 head, no neck or tubercle, and are pointed at the free extremity. The 

 eleventh has a slight ridge, representing the angle, and a shallow 

 groove on the lower border ; the twelfth has neither. 



* This groove is commonly described as supporting the intercostal artery 

 vein and nerve, but this is not the case. 



