120 OSTEOLOGY. 



THE COSTAL CAKTILAGES. 



The Costal Cartilages (fig. 69) are white elastic structures, which serve to pro- 

 long the ribs forward to the front of the chest, and contribute very materially to 

 the elasticity of this cavity. The first seven are connected with the sternum, the 

 next three with the lower border of the cartilage of the preceding rib. The 

 cartilages of the last two ribs, which have pointed extremities, float freely in the 

 walls of the abdomen. Like the ribs, the costal cartilages vary in their length, 

 breadth, and direction. They increase in length from the first to the seventh, then 

 gradually diminish to the last. They diminish in breadth, as well as the intervals 

 between them, from the first to the last. They are broad at their attachment to 

 the ribs, and taper towards their sternal extremities, excepting the first two, which 

 are of the same breadth throughout, and the sixth, seventh, and eighth, which are 

 enlarged where their margins are in contact. In direction they also vary ; the 

 first descends a little, the second is horizontal, the third ascends slightly, whilst all 

 the rest follow the course of the ribs for a short extent, and then ascend to the 

 sternum or preceding cartilage. Each costal cartilage presents two surfaces, two 

 borders, and two extremities. The anterior surface is convex, and looks forwards 

 and upwards ; that of the first gives attachment to the costo-clavicular ligament ; 

 that of the first, second, third, fourth, fifth, and sixth, at their sternal ends, to the 

 Pectoralis major. The others are covered, and give partial attachment to some 

 of the great flat muscles of the abdomen. The posterior surface is concave, and 

 directed backwards and downwards, the six or seven inferior ones affording 

 attachment to the Transversalis and Diaphragm muscles. Of the two borders, 

 the superior is concave, the inferior convex ; they afford attachment to the Inter- 

 costal muscles, the upper border of the sixth giving attachment to the Pectoralis 

 major muscle. The contiguous borders of the sixth, seventh, and eighth, and 

 sometimes the ninth and tenth costal cartilages, present smooth oblong surfaces at 

 the points where they articulate. Of the two extremities, the outer one is con- 

 tinuous with the osseous tissue of the rib to which it belongs. The inner extremity 

 of the first is continuous with the sternum ; the six succeeding ones have rounded 

 extremities, which are received into shallow concavities on the lateral margins of 

 the sternum. The inner extremities of the eighth, ninth, and tenth costal carti- 

 lages are pointed, and lie in contact with the cartilage above. Those of the 

 eleventh and twelfth are free, and pointed. 



The costal cartilages are most elastic in youth, those of the false ribs being 

 more so than the true. In old age, they become of a deep yellow color. Under 

 certain diseased conditions, they are prone to ossify. Mr. Humphry's observa- 

 tions on this subject have led him to regard the ossification of the costal cartilages 

 as a sign of disease rather than of age. " The ossification takes place in the first 

 cartilage sooner than in the others ; and in men more frequently, and at an earlier 

 period of life, than in women." 



Attachment of Muscles. The Subclavius, Sterno-thyroid, Pectoralis major, 

 Internal oblique, Transversalis, Bectus, Diaphragm, Triangularis sterni, Internal 

 and External intercostals. 



OF THE EXTEEMITIES. 



The Extremities or limbs are those long-jointed appendages of the body, which 

 are connected to the trunk by one end, being free in the rest of their extent. 

 They are four in number : an upper or thoracic pair, connected with the thorax 

 through the intervention of the shoulder, and subservient mainly to tact and pre- 

 iiension ; and a lower pair, connected with the pelvis, intended for support and 

 locomotion. Both pairs oi 1 limbs are constructed after one common type, so that 

 they present numerous analogies ; while, at the same time, certain differences are 

 observed in each, dependent on the peculiar offices they severally perform. 



