Intercostal Arteries 149 



Where the manubrium joins the gladiolus there is a tratisverse 

 ridge which is easily felt on running the finger down the middle line. 

 The cartilages at the ends of the ridge are those of the second ribs. 

 In counting the ribs in a fat subject it is convenient to remember this. 

 The ridge corresponds also with the lower border of the second part of 

 the aortic arch. 



Fracture of tJie sternum generally results from the chin being 

 forcibly doubled into the chest, as in a fall on the head, the springi- 

 ness of the ribs saving it from fracture from direct violence. Occa- 

 sionally the manubrium is dislocated forwards over the gladiolus. 



Of the ribs, seven articulate with sternum, but the lower five do 

 not ; the eleventh and twelfth, being free anteriorly, are rarely broken. 

 The first rib is rarely broken, unless the clavicle, which protects it, 

 have first yielded. The ribs most often broken are the middle ones, 

 and the seat of fracture is generally in front of their angle. A rib may 

 be broken by direct violence, as by a blow with the fist, in which case 

 the salient angle is more apt to damag'e the pleura and lung, than 

 when the fracture is from indirect violence, as when a man is crushed 

 against a wall, in which case damage to the pleura and lung occurs 

 only when several ribs have been broken. When a man with fractured 

 ribs spits brig'ht and frothy, bloody sputa, there is evidently a wound of 

 the lung ; possibly also pneumothorax exists. 



The groove along the lower part of the inner surface of the rib con- 

 tains the intercostal arteiy, with the vein above it and the nerve below, 

 passing between the inner and outer intercostal muscles ; to avoid 

 these, in puncturing the chest, the trocar should neither be introduced 

 through the upper part of the intercostal space nor through the lower, 

 where the collateral branch is coursing. In medio ttitissimus ibis. 



The intercostal arteries come from the superior intercostal of the 

 subclavian, from the aorta, and from the internal mammary; they 

 anastomose freely with branches of the axillary and send emissaries 

 through the spaces to supply the mamma ; a wounded intercostal 

 artery may bleed into the pleural cavity (hcemothorax). If the skin 

 be also wounded the artery may be compressed by the finger passed 

 in under the rib. 



The costal cartilage fits in a depression at the end of the rib ; the 

 other end articulates with the sternum, and, with the exception of the 

 first cartilage, which fuses with the manubrium, each chondro-sternal 

 joint has a synovial membrane. Indeed, the joints of the second and 

 third cartilages usually have each two membranes. As the result of 

 injury either end of a costal cartilage may be detached. Comparative 

 anatomy shows that the cartilages are anterior epiphyses. 



The cartilages from the sixth to the ninth are connected with each 

 other by capsular ligaments lined by synovial membranes. 



Most of the ribs articulate by their head with the bodies of two 

 vertebrae and with the intervertebral disc, being connected by the 



