THE RIBS. 27 



and angle. The curve of the ribs is more marked towards the back part than in 

 front, especially near the angle. Besides the main curves now mentioned, the rib 

 is slightly twisted on itself, so that while its surfaces are vertical behind, they are 

 placed somewhat obliquely in front. 



Special characters of certain ribs. The ribs increase in length from the 

 first to the seventh or eighth, and decrease to the twelfth, so that the last is little 



MIIMEIMCE FOR SERRATUS MAGNUS 



Fig. 27. FlKST AND SECOND RIBS OF THE EIGHT SIDE, FROM ABOVE. 



(Drawn by D. Gunn.) f 



longer, often even shorter, than the first. The first rib is the broadest, and after it 

 the middle ones ; the twelfth is the narrowest. The distance of the angle from 

 the tuberosity increases gradually from above down. 



The first rib is hot twisted, and is so placed that its surfaces look nearly upwards 

 and downwards. The head is small, and presents a single articular surface for the 

 first dorsal vertebra. The neck is slender, and the angle coincides with the 

 tuberosity. On the superior surface are two slight smooth depressions with an 

 intervening rough mark, and a considerable rough surface behind. The rough 

 surface marks the attachment of the scalenus medius muscle, the posterior depression 

 the position of the subclavian artery, the anterior depression the subclavian vein ; 

 and the intervening slight elevation, frequently terminating in a sharp spine on the 

 inner edge the scalene tubercle indicates the attachment of the scalenus anticus 

 muscle. There is no subcostal groove on the first rib. 



The second rib, longer than the first, presents externally a prominent roughness 

 which marks the attachment of the serratus magnus. 



In the eleventh and twelfth ribs the articular facet on the head is single, and 

 the tuberosity is represented only by a slight elevation or roughness, without an 

 articular facet. The subcostal groove is faintly marked on the eleventh, and is 

 absent, together with the angle, from the twelfth. 



Varieties. The number of the ribs is sometimes increased to thirteen on one or both 

 sides. The supernumerary rib is usually short, and is most frequently formed in connection 

 with the transverse process of the first lumbar vertebra, or occasionally with the seventh 

 cervical ; in the latter case the additional rib has generally a double attachment, viz., to the 

 body, and to the transverse process of the vertebra outside a vertebrarterial foramen (see 

 fig. 23, 4, v, v, and 8, <?0). In rare instances the additional rib is associated with a 

 thirteenth dorsal vertebra (see p. 13). The tenth rib frequently articulates only with 



