•28 BONES OF THE THORAX. 



two vertebrae, and, between them, a slight ridge, to which the inter- 

 articular ligament is attached. At a little distance from the head, and 

 separated from it by the slightl}' constricted neck, is the tubercle, which 

 is directed backwards, and presents a smooth surface for articulation 

 with the transverse process of the inferior of the two vertebra with 

 which the head is connected, and, outside that, a roughness marking 

 the insertion of the posterior costo-transverse ligament. The whole 

 extent beyond the tubercle constitutes the hodij. It is laterally com- 

 pressed, and broader from above downwards towards the anterior 

 extremity. Outside the tubercle, between it and the most convex part 

 of the body, is a rough line, which corresponds to the outer border of 

 the erector spinte muscle, and marks the angle, so-called because at this 

 point the rib takes a more sudden curve, its direction being now for- 

 wards and outwards. The inferior border presents on its inner aspect 

 the f!i(hcostaI e/roove, in which lie the intercostal vessels and nerve, and 

 ■which is best marked opposite the angle, and disappears in ft'ont. The 

 ^anterior extremity is hollowed at its tip into an oval pit, in which the 

 costal cartilage is implanted. 



Indination and Curves. — There is a general inclination of the ribs 

 •downwards from the head to the anterior extremity, the slope being 

 ■greatest between the head 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 somewhat 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 eighth, and decrease from the ninth to the 

 twelfth, so that the last is little 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 tul)ercle 

 increases gradually from the second to the eleventh ; in the first the 

 angle coincides with the tubercle, in the last it is efTaced. 



Theirs/ rib is not twisted, and is so placed that its superficial and 

 deep surftices look respectiA^ely nearly upwards and downwards. The 

 head is small, and presents a single articular surface. The neck is round 

 and slender. It articulates with the body and transverse process of the 

 first dorsal vertebra alone. On the superior surface are two very slight 

 .smooth depressions with an intervening rough mark, and a considerable 

 rough surface behind. The rough surface marks the attachment of the 

 scalenus mcdius 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. 



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

 roughness which marks the attachment of the serratus magnus. 



The eleventh and fwelffJi ribs have no groove on the inferior border, 

 no articular facet on the tubercle, and only a single articulating surface 

 •on the head. The mark of the angle is scarcely perceptible on the 

 <^leventh, and is absent from the twelfth. 



Viirictitv. — Tlie number of tlie ribs is sometimes increased to thirteen on one 

 or both sides. The supernumerary rib is most frequently very short, and is 



