io8 THE RIBS. [CHAP. 



The vertebral ribs, when in their most typical condition, 

 have two points of attachment to the vertebrae : the tubercle 

 (tuberculum) and the head (capituluni). The former is 

 superior or dorsal and posterior, and attached to the trans- 

 verse process of the vertebra ; the latter, inferior or ventral 

 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 neurocentral 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 capituluni (at least in the anterior ribs) is 

 placed opposite to the intervertebral space in front of this 

 vertebra, and portions of two vertebrae 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 vertebrae / 



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, 



