242 



THE ARTICULATIONS 



on its own axis. There is no interarticular ligament in the costo-vertebral joints 

 of the first, tenth, eleventh, and twelfth ribs. 



The radiate (or stellate) ligament, a thickening of the anterior part of the 

 capsule (figs. 280 and 281), is the most striking of all, and consists of bright, 

 pearly-white fibres attached to the anterior surface, and upper and lower borders 

 of the neck of the rib, a little way beyond the articular facet; from this they 

 radiate upward, forward, and downward, so as to form a continuous layer of 

 distinct and sharply defined fibres. 



The middle fibres run straight forward to be attached {g the intervertebral disc; the upper 

 ascend to the lower half of the lateral surface of the vertebra above, and the lower descend to 

 the upper half of the vertebra below. The radiate ligament is overlapped on the vertebral 

 bodies by the lateral (short) vertebral ligaments. 



In the case of the first, tenth, eleventh, and twelfth ribs, each of which articulates with one 

 vertebra, the ligament is not quite so distinctly radiate, but even in these the ascending fibres 

 reach the vertebra above that with which the rib articulates. 



Fig. 



280. — Showing the Anterior Longitudinal Ligament, and the Connection of the 

 RtBS WITH the Vertebra. 



The interarticular ligament 



Thecosto-transverse ligaments 



E^] — The radiate ligament 



The synovial membranes (fig. 281) consist of two closed sacs which do not 

 communicate: one above, and the other below, the interarticular ligament. In 

 the case of the first, tenth, eleventh, and twelfth articulations, there is but one 

 synovial membrane, as these joints have no interarticular ligament. 



The arterial supply is from the intercostal arteries, the twigs piercing the radiate and 

 capsular ligaments. 



The nerve -supply comes from the anterior primary branches of the intercostal nerves. 



Those joint.s approach most nearly in their movements to the condylarthroses. 



The movements arc ginglymoid in character, consisting of a slight degree of elevation and 

 depression around an oblif|uely horizontal axis corresponding with the interarticular ligament; 

 there is also a slight amount of forward and backward gliding; and a slight degree of screwing or 

 rotatory movement \» also possible. There is a considerable difference in the degree of mobility of ^ 

 the different rit)s, for while the first rib is almost immobile except in a very deep inspiration,'^ '0 

 the mobility of the others increa.ses from the second to the last; the two floating ribs being the 

 most mobile of all. The head of the rib is the most fixed point of the costal arch, and upon 

 it the whole arch rotates; the interarticular ligament allows only a very limited amount of 

 flexion and extension (i. e., elevation and depression), and of gliding. Gliding is checked by 

 the radiate ligament. 



In inspiration, the rib is elevated, and glides forward in its socket, too great elevation 

 being checked not oidy by the ligaments, but uLst) l)y the overhanging upper edge of the cavity 

 itself. In expiration, the rib is depressed, and glides backward in its cavity. 



