COSTAL CARTILAGES. 7-5 



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 upwards. In advanced age the costal 

 cartilages are mare 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 consolidated with the rest of the bone at twenty-five. 



Articulations. Each rib articulates with two vertebra, and one 

 costal cartilage, with the exception of the first, tenth, eleventh, and 

 twelfth, which articulate each with a single vertebra only. 



Attachment of Muscles. To the ribs and their cartilages are attach- 

 ed twenty-iico pairs, and one single muscle. To the cartilages, the 

 subclavius, sterno-thyroid, pectoralis major, internal oblique, rectus, 

 transversalis, diaphragm, triangularis sterni, internal and external in- 

 tercostals. To the rz'As, the intercostal muscles, scalenus anticus, 

 scalenus posticus, pectoralis minor, serratus magnus, obliquus externus, 

 obliquus internus, latissimus dorsi, quadratus lumborum, serratus posti- 

 cus superior, serratus posticus inferior, sacro-lumbalis, longissimus dorsi, 

 cervicalis ascendens, levatores costarum, transversalis, and diaphragm. 



CLAVICLE. The clavicle is a long bone shaped like the italic letter 

 f, and extended across the upper part of the side of the chest from the 

 upper piece of the sternum to the point of the shoulder, where it arti- 

 culates with the scapula. In position it is very slightly oblique, the 

 sternal end being somewhat lower and more anterior than the scapular, 

 and the curves are so disposed that at the sternal end the convexity, 

 and at the scapular the concavity, is directed forwards. The sternal 

 half of the bone is rounded or irregularly quadrilateral, and terminates 

 in a broad articular surface. The scapular half is flattened from above 

 downwards, and broad at its extremity, the articular surface occupying 

 only part of its extent. The upper surface is smooth and convex, and 

 partly subcutaneous ; while the under surface is rough and depressed, 

 for the insertion of the subclavius muscle. At the sternal extremity 

 of the under surface is a very rough prominence, which gives attach- 

 ment to the rhomboid ligament ; and at the other extremity a rough 



