J02 COSTAL CARTILAGES. 



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 corresponding vertebra. The vertebral 

 end of the rib is somewhat expanded, 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 transverse ridge into 

 two facets, for articulation with two contiguous vertebrae. The posterior 

 surface of the neck is rough, for the attachment of the middle costo-trans- 

 verse ligament ; and upon its upper border is a crest, which gives attach- 

 ment 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. 



Thejirst 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 in- 

 ternal border, is a tubercle which gives attachment to the scalenus anticus 

 muscle, and immediately before and behind this tubercle, a shallow ob- 

 lique 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 surface for the transverse pro- 

 cess of the first dorsal vertebra. There is no angle. Beyond the tuber- 

 osity is a narrow constricted neck ; and at the extremity, a head, present- 

 ing 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 H shallow groove 

 on the lower border ; the twelfth has neither. 



COSTAL CARTILAGES. The costal cartilages 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 the opposite extremity ; they diminish gradually 

 in breadth from the first to the last ; in length they increase from the first 

 to the seventh, and then decrease to the last. The cartilages of the first 

 two ribs are horizontal in direction, the rest incline more and more up- 

 w r ards. In advanced age the costal cartilages are more or less converted 

 into bone, this change taking place earlier in the male than in the female. 



The first seven cartilages articulate with the sternum ; the three next 

 with the lower border of the cartilage immediately preceding, while the 

 last two lie free between the abdominal muscles. All the cartilages of the 

 false ribs terminate by pointed extremities. 



Development. The ribs are developed by three centres ; one for the 

 central part, one for the head, and one for the tubercle. The last two 

 have no centre for the tubercle. Ossification commences in the body 

 somewhat before its appearance in the vertebrae ; the epiphysal centres for 

 the head and tubercle appear between sixteen and twenty, and are conso- 

 lidated with the rest of the bone at twenty-five. 



