

THE RIBS 



125 



inferior border, but just in front of the angle, where it is deepest and broadest, it is 

 on the internal surface. The superior edge of the groove is rounded and serves 

 for the attachment of an Intercostalis internus; the inferior edge corresponds to 

 the lower margin of the rib, and gives attachment to an Intercostalis externus. 

 Within the groove are seen the orifices of numerous small foramina for nutrient 

 vessels which traverse the shaft obliquely from before backward. The superior 

 border, thick and rounded, is marked by an external and an internal lip, more 

 distinct behind than in front, which serve for the attachment of Intercostales 

 externus and internus. The inferior border is thin, and has attached to it an Inter- 

 costalis externus. 



Anterior Extremity. The anterior or sternal extremity is flattened, and presents a 

 porous, oval, concave depression, into which the costal cartilage is received. 



Peculiar Ribs. The first, second, tenth, eleventh, and twelfth ribs present 

 certain variations from the common .characteristics described above, and require 

 special consideration. 



' Demifacet for vertebra, 



Interarticular crest 

 Demifacet for vertebra, 



Articular part of tubercle 

 Non-articular part of tubercle 



Costal groove 



FIG. 123. A central rib of the left side, viewed from behind. 



First Rib. The first rib (Fig. 124) is the most curved and usually the shortest 

 of all the ribs; it is broad and flat, its surfaces looking upward and downward, 

 md its borders inward and outward. The head is small, rounded, and possesses 

 only a single articular facet, for articulation with the body of the first thoracic 

 vertebra. The neck is narrow and rounded. The tubercle, thick and prominent, 

 is placed on the outer border. There is no angle, but at the tubercle the rib is 

 slightly bent, with the convexity upward, so that the head of the bone is directed 

 downward. The upper surface of the body is marked by two shallow grooves, 

 separated from each other by a slight ridge prolonged internally into a tubercle, 

 the scalene tubercle, for the attachment of the Scalenus anterior; the anterior 

 grooA r e transmits the subclavian vein, the posterior the subclavian artery and 

 the lowest trunk of the brachial plexus. 1 Behind the posterior groove is a rough 

 area for the attachment of the Scalenus medius. The under surface is smooth, 

 and destitute of a costal groove. The outer border is convex, thick, and rounded, 

 and at its posterior part gives attachment to the first digitation of the Serratus 

 anterior; the inner border is concave, thin, and sharp, and marked about its center 

 by the scalene tubercle. The anterior extremity is larger and thicker than that 

 of any of the other ribs. 



Second Rib. The second rib (Fig. 125) is much longer than the first, but has a 

 very similar curvature. The non-articular portion of the tubercle is occasionally 





1 Anat. Anzeiger, 1910, Band xxxvi. 



