72 COSTAL CARTILAGES. 



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 tuberosity ; and 

 immediately at the base and rather below the tuberosity a smooth 

 surface for articulation with the .extremity of the transverse pro- 

 cess of the corresponding vertebra. Beyond the tuberosity is the 

 neck ; and at the extremity of the neck an oval surface, the head, 

 divided by a ridge into two facets for articulation with two con- 

 tiguous vertebrae. The posterior surface 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, and the 

 three last. 



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

 zontally at the upper part of the thorax, the surfaces looking up- 

 wards 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 at- 

 tachment 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 tube- 

 rosity, with a smooth articular surface for the transverse process of 

 the first dorsal vertebra. There is no angle. Beyond the tube- 

 rosity is a narrow constricted neck ; and quite at the extremity, a 

 head, presenting a single articular surface. The second rib ap- 

 proaches 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 tuberosity, and are pointed at the extremity. 

 The eleventh has a slight ridge, representing the angle, and a shal- 

 low groove on the lower border ; the twelfth has neither. 



COSTAL CARTILAGES. The costal cartilages (fig. 27. 11, 11) serve 

 to prolong the ribs forwards to the anterior part of the chest, and 

 contribute mainly to the elasticity of the thorax. They are broad 

 at their attachment to the ribs, and taper slightly towards their oppo- 

 site extremities ; they gradually diminish in breadth from the first to 

 the last, and increase in length from the first to the seventh, and then 

 diminish to the last. 



The seven first cartilages articulate with the sternum; the three 

 next with the lower border of the cartilage immediately preceding. 

 All the cartilages of the false ribs terminate by pointed extremities. 



Developement. The ribs are developed by three centres ; one for 



