viii] GENERAL CHARACTERS. • 89 



{tuberculuni) and the head {capitulum). The ' former is 

 superior and posterior, and attached to the transverse pro- 

 cess of the vertebra ; the latter, inferior and anterior, and 

 attached to the body of the vertebra, or the inferior part of 

 the arch near the body, and always very near the neuro- 

 central suture. Commonly, in fact, the articular surface is 

 cut by this suture. Sometimes, as in Man, the greater part 

 of the articulation is above the suture ; or, on the other 

 hand, it may be, as in the Monotremes, below the suture. 

 The distinction between the two points of attachment is 

 most marked in the anterior ribs; in passing backwards 

 they approach nearer to each other, sometimes becoming 

 blended, or sometimes either one or the other (generally 

 the tubercular) attachment is lost in the hindermost ribs. 



The tubercle articulates, by a nearly flat or slightly con- 

 vex surface, to a facet on the under-surface of the extremity 

 of the transverse process of the corresponding vertebra, but 

 the more rounded capitulum (at least in the anterior ribs) is 

 placed opposite to the intervertebral space in front of this 

 vertebra, and portions of two vertebras commonly contribute 

 to form the articular cavity for its reception. Thus the first 

 rib is articulated by its tubercle to the transverse process of 

 the first thoracic vertebra, and by its head to the hinder 

 part of the seventh cervical, and front part of the first 

 thoracic vertebra, and so on. The posterior ribs, as a rule, 

 are connected solely with their own corresponding ver- 

 tebrae. 



The amount of motion permitted by these articulations 

 is sufficient to allow the thorax to expand and contract in 

 respiration. In inspiration the ribs are drawn forwards, and 

 approach nearer to a right angle with the vertebral column ; 

 while in expiration they fall back, and occupy a more 

 oblique position to the axis of the column. 



