LIGAMENTS OF THE RIB. 345 



ribs being free anteriorly, and not fixed behind by a joint to the transverse 

 process. 



During the increase and decrease of the chest the body of the rib is 

 rotated out and in, around a line subtending the arc of the circle of which 

 its fore part is a segment. The degree of motion is greatest in the long- 

 est ribs. 



LIGAMENTS OF THE NECK AND TUBERCLE. Three ligaments (costo- 

 transverse) pass from the neck and tubercle of the rib to two transverse 

 processes. And there is a synovial sac between the rib and its transverse 

 process. 



The anterior costo transverse ligament (fig. 108, 4 ) is larger and longer 

 than the others. It ascends from the upper edge of the neck to the trans- 

 verse process of the upper of the two vertebrae with which the head articu- 

 lates : it is wanting to the first rib. Between this ligament and the verte- 

 bra the posterior branches of the intercostal vessels and dorsal nerve pass ; 

 and externally it is joined by the fibrous membrane between the strata of 

 the intercostal muscles. 



The posterior costo -transverse (fig. 115, 3 ) is placed at the posterior 

 aspect of the rib. It is a short band of fibres between the rougli part of 

 the tubercle and the tip of the transverse process of the lower of the two 

 vertebras touched by the rib head. This band is longest in the lowest 

 two articulations. 



The middle or interosseous costo-transverse is placed horizontally be- 

 tween the neck of the rib and the transverse process with which the 

 tubercle articulates. It will be best seen by sawing horizontally through 

 the rib and the transverse process. Its fibres are mixed with reddish 

 areolar tissue. 



In the lowest two ribs the interosseous costo-transverse blends in one 

 band with the posterior costo-transverse ligament. 



Synovial sac. If the posterior ligament is divided, a synovial mem- 

 brane will be exposed in the joint between the tubercle of the rib and the 

 transverse process. 



In the lowest two ribs, which do not touch transverse processes, the 

 synovial sac is absent. 



Movement. In the motion of the rib, the bone glides upwards and 

 downwards on the articular facet of the transverse process ; and the degree 

 will be limited by the surrounding costo-transverse ligaments. 



LIGAMENTS OF THE STERNAL CARTILAGES. The cartilages of the 

 true ribs except the first are united to the sternum by a fibrous capsule, 

 which covers a synovial membrane; and externally they are joined to the 

 osseous part of the rib. The first is generally ossified to the sternum ; 

 and some of the lower cartilages touch each other, and are connected to- 

 gether by fibrous bands with synovial membranes. 



In the chondro-sternal articulation (fig. 51, 4 ), the cartilages are re- 

 ceived into the depressions on the side of the sternum, and are fixed in 

 their position by a capsule of surrounding fibres. In front and behind 

 the capsule are thickened bands, which have been described as anterior 

 and posterior ligaments. 



Between the cartilage and the bone is a synovial membrane. 



In the joint of the second cartilage there is an mterarticular ligament 

 (fig. 51, 6 ), as in the head of the rib, which joins the cartilage between 

 the pieces of the sternum. A synovial sac exists on each side of the 

 interarticular ligament. 



