I70 HUMAN ANATOMY. 



rib, and ends at or near the region mentioned, pain being often referred to the 

 peripheral ends of sensory nerves. 



In fractures by indirect violence (when the sternum and spine are forced 

 together), the theoretical point of fracture would be at or about the summit of the 

 arch ; but practically it is often found very near the point at which the force is apt 

 to be received, — i.e., an inch or two outside of the sternal extremity. 



Unless the force has been great, there is but little displacement in fracture of a 

 rib, owing to the splinting of the bone between the two sets of intercostal muscles 

 above and below it. Shortening is absent, unless an extensive crush of the whole 

 side of the chest has occurred, because the two ends of the bone are fixed, and 

 because of the unbroken bones above and below the fractured one. The complica- 

 tions are those obviously due to the proximity of the pleura and lung on the inner 

 surface of the fracture, the common results of wounds of those structures being 

 various degrees of haemothorax, or pneumothorax, or sometimes (by valvular action) 

 emphysema of the cellular tissue of the trunk (page 1865). 



Broken ribs always unite with a considerable amount of ensheathing or pro- 

 visional callus, due to the motion which to some degree must be present between 

 the fragments during the process of union. 



Rupture of an intercostal artery (unless associated with a wound of the pleura) 

 is not usually a serious complication ; but occasionally it is necessary to arrest 

 hemorrhage from this vessel. It lies between the inner and outer intercostal muscles 

 in the groove running along the lower part of the inner surface of each rib. The 

 collateral branch runs near the upper surface of the ribs. Midway between the ribs 

 is, therefore, the safest place to introduce a trocar or to make an incision in opening 

 the chest. The intercostal spaces are wider in the antero-lateral parts of the chest 

 than they are more posteriorly, especially in the neighborhood of the seventh rib ; 

 they are narrowest in close proximity to the sternum and spine. They can be 

 widened by bending the body to the opposite side. 



For paracentesis of the thorax the centre of the sixth or seventh space should be 

 selected in the mid-axillary line. The lower spaces are in too close proximity to the 

 diaphragm, especially on the right side. More anteriorly it is also in danger ; farther 

 posteriorly the intercostal artery (which runs more iiorizontally than the ribs) 

 crosses the space obliquely, and behind the angles the ribs are covered by the thick 

 muscles of the back. 



The ribs are frequently subject to infectious disease. Syphilis and tubercu- 

 losis often produce periostitis or caries, and they are more often the seat of post- 

 typhoidal osteitis than any other bones of the skeleton. This is due to their 

 subcutaneous position exposing them to frequent traumatisms and to the similar 

 effects produced by the numerous strains through muscular action in coughing and 

 sneezing and in lifting or straining. 



Pus is very apt to travel along the loose connective tissue between the two planes 

 of intercostal muscles, and it is therefore unusual to find suppurative disease confined 

 to one rib, or even to the immediate vicinity of its point of origin. 



No instance of traumatic separation of the epiphysis of either the head or the 

 tuberosity of a rib has been recorded. 



The internal mammary artery runs from above downward beneath the cartilages 

 about half an inch from the sternum. 



Landmarks. — The oblique elevations formed by the ribs can usually be seen 

 extending downward from the axillary region. The upper ribs are covered by the 

 great pectoral, but beneath its lower border the ribs from the sixth to the tenth 

 can often be seen. The lower border of the great pectoral follows the direction of 

 the fifth costal cartilage. 



The curved arch of the costal cartilages is frequently plainly visible, and is 

 accentuated during forced expiration and when a superincumbent weight is held up 

 by the trunk and arms. In short persons the arch is commonly flatter than in tall 

 ones. 



In counting the ribs it is well to begin with the second, which is easily identified 

 by its relation to the ridge between the manubrium and body of the sternum. 



The nipple is usually over the fourth intercostal space, somewhat less than 2.5 



