152 



HUMAN ANATOMY. 



The ribs increase in length from the first to the seventh or eighth, after which 

 they decrease to the last, which is usually the shortest. The length of the last rib 

 is, however, very uncertain, varying from one centimetre to perhaps fifteen centime- 

 tres or more. It often is longer than the first. The curve is comparatively 

 regular in the first rib, after which the difference between the two ends becomes 

 more marked, the curve being very pronounced behind and less so in front. The 

 curve is much less throughout in the lower ribs ; in fact, it decreases continually. 

 The first rib is the broadest of all at the anterior end. There is a general, but not 

 regular, increase from the second to the seventh rib, and a subsequent decrease. 

 The fourth rib is relatively broad, the fifth narrow.' 



Exceptional Ribs. — Certain of the ribs — the first, second, tenth, eleventh, 

 and twelfth — present peculiarities which claim mention. 



Fig. 176. 



Head -J 



Neck 



Articular — 

 facet on tu- 

 bercle 



Accessorius 



Angle 



External 

 intercostal 



Second digitation of serratus magnua 

 Third digitation of serratus magnus 

 First and second ribs of right side, upper surface. 



The first rib is flat, not twisted, with, an outer and an inner border. The 

 head is small and has but one facet, resting as it does on the first thoracic vertebra. 

 The neck is small and flat like the body. The tubercle is very prominent. The 

 scalene tubercle is a very small but, from its relations, important elevation on the 

 inner margin of the upper surface, at about the middle, for the insertion of the 

 scalenus anticus. It separates two grooves crossing the bone for the subclavian 

 artery and vein. The posterior one for the artery is the more marked. There is a 

 rough impression behind the latter near the outer border for the scalenus medius. 

 There is no subcostal groove. 



The second rib is intermediate in shape between the first and the rest. The 

 roughness for the serratus magnus is very marked about the middle of the shaft. 



* Anderson : Journal of Anatomy and Physiology, vol. xviii., 1884. 



