332 THE ARTICULATIONS. 



posterior branches of the intercostal vessels and nerves. Its external border is 

 continuous with a thin aponeurosis which covers the External intercostal muscle. 



The first rib has no anterior costo-transverse ligament. 



The Middle Costo-transverse or Interosseous Ligament consists of short but 

 strong fibres which pass between the rough surface on the posterior part of the 

 neck of each rib and the anterior surface of the adjacent transverse process. In 



ANTERIOR COSTO-TRANSVERSE 



LIGAMENT DIVIDED. 



or INTEHOSSEOUS 



POSTERIOR COSTO- 

 TRANSVERSE LIGAMENT 



FIG. 236. Costo-transverse articulation. Seen from above. 



order fully to expose this ligament, a horizontal section should be made across the 

 transverse process and corresponding part of the rib ; or the rib may be forcibly 

 separated from the transverse process and its fibres put on the stretch. 



In the eleventh and twelfth ribs this ligament is quite rudimentary or 

 wanting. 



The Posterior Costo-transverse Ligament is a short but thick and strong fascic- 

 ulus which passes obliquely from the summit of the transverse process to the 

 rough non-articular portion of the tubercle of the rib. This ligament is shorter 

 and more oblique in the upper than in the lower ribs. Those corresponding to 

 the superior ribs ascend, while those of the inferior ribs descend slightly. 



In the eleventh and twelfth ribs this ligament is wanting. 



The Capsular Ligament is a thin, membranous sac attached to the circumference 

 of the articular surfaces, and enclosing a small synovial membrane. 



In the eleventh and twelfth ribs this ligament is absent. 



Actions. The heads, necks, and tubercles of the ribs are so closely connected 

 to the bodies and transverse processes of the vertebrae that only a slight gliding 

 movement of the articular surfaces on each other can take place in these articu- 

 lations. The result of this gliding movement is for the upper six ribs an ele- 

 vation of the front and middle portion of the rib, the hinder part being pre- 

 vented from performing any upward movement by its close connection with the 

 spine. In this gliding movement the rib rotates on an axis corresponding with 

 a line drawn through the two articulations, Costo-central and Costo-transverse, 

 which the rib forms with the spine. Of the four succeeding ribs, each one, 

 besides rotating on the above-mentioned axis, also rotates on an axis corre- 

 sponding with a line drawn from the head of the rib to the sternum. In other 

 words, an upivard and backward gliding is permitted between tubercle and trans- 

 verse process, owing to the especial degree of obliquity existing between the corre- 



