210 



THE A R TIC I LA TIOXS 



The nerve-supply cxints t'roin the anterior primary hranches of the intercostal 

 nerves. 



These joints api^-oach most nearly in their movements to the condylarth roses. 



The movements are ginglymoid in character, consisting of a sHght degree of 

 elevation and depression around an ol)liquely horizontal axis corresponcHng with 

 the interarticular hgament; there is also a shght amount of forward and Ixickward 

 gliding; and a slight degree of screwing or rotatory movement is also possible. 

 There is a consideral)le dilference in the degree of mobility of the different ribs, for 

 while the first rib is almost immobile except in a very deep inspiration, the mobility 

 of the others increases 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 ui>on it the whole arch rotates; the interarticular ligament allows only a very 



Fig. 216.— Horizontal Section' through the Intervertebral Disc and Ribs. 



Anterior costo-central 

 or Btellate ligament 



Costo-central synovial 

 sac 



Middle costo-trans- 

 verse ligament 



Laminar portion of inter- 

 vertebral disc 



Central pulpy portion of inter- 

 vertebral disc 



Costo-tranaverse synovial sac 



Posterior costo-trausverse 

 ligament 



limited amount of flexion and extension (i.e. elevation and depression), and of 

 gliding. Gliding is checked by the stellate ligament. 



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

 elevation being checked not only by the ligaments, but also by the overhanging 

 upper edge of the cavity itself. In expiration, the rib is depressed, and glides 

 Ijackwards in its cavitv. 



(/;) The Costo-transverse Articulation 

 Class. — Di'ivthro.-ii.-i. Subdivision. — Arthrodia. 



This joint is formed by the tubercle of the rib articulating with the anterior part 

 of the tip of the transverse process. The eleventh and twelfth ribs are devoid of 

 tliese joints, for the tubercles of these ribs are absent, and the transverse processes 

 of the eleventh and twelfth thoracic vertebrae are rudimentary. 



The ligaments of the union are: — 



Capsular. 



Middle costo-transverse. 



Su])erior costo-transverse. 

 P( )st('rior costo-transverse. 



The capsular ligament ( ligs. 214 and 21G) forms a thin, loose, fil)rous 

 envelope to the synovial membrane. Its filjres are attached to the bones just 

 beyond the articular margins, and arc thickest below, where they are not strength- 

 ened by any other structure. It is connected on the inner side with the middle, 



