ARTICULATIONS OF THE RIBS. 491 



and the tuberosity forms a synovial joint with the transverse process 

 of the lower vertebra. 



The superior costo-transverse ligament (fig. 177, 4 ) is larger and superior or 

 longer than the others. It ascends from the upper edge of the neck ascendlll 8> 

 of the rib to the transverse process of the vertebra above : it is 

 wanting to the first rib. Between this ligament and the vertebra 

 the posterior branches of the intercostal vessels and nerves pass ; and 

 externally it is continued into the posterior intercostal aponeurosis. 



The posterior costo-transverse ligament (fig. 184, 3 , p. 497) is a short posterior, 

 band of fibres between the rough part of the tuberosity of the rib 

 and the tip of the transverse process with which the latter articulates. 



The middle or interosseous costo-transverse ligament is placed and middle ; 

 between the neck of the rib and the transverse process which the 

 tuberosity touches. It will be best seen by sawing horizontally 

 through the rib and the transverse process. Its fibres are collected 

 into separate bundles, with fatty tissue between them. 



The synovial cavity of the costo-transverse articulation will be synovial 

 opened by dividing the posterior ligament. sac - 



There is no joint between the last two ribs and their transverse Differences 

 processes ; and the posterior and middle costo-transverse ligaments 

 are united in one band. ribs 



Movements of the ribs. The ribs undergo a movement of rotation The ribs 

 around an axis which passes through the costo-central articulation JJJund an 

 in a direction corresponding very nearly to that of the neck of the axis, 

 bone. By this rotation the fore part of the rib is carried upwards 

 and outwards in inspiration, and downwards and inwards in 

 expiration. The degree of outward movement is necessarily pro- which is 

 portionate to the obliquity of the axis, and is therefore greater in 

 the case of the lower ribs than the upper, since the backward 

 inclination of the transverse process of the dorsal vertebrae, and of 

 the necks of the ribs, increases from above downwards. The lower The lower 

 ribs, while being elevated, also move somewhat backwards, their one ^ also , 

 tuberosities gliding over the sloped facets of the transverse processes ; wards and 

 and in the eleventh and twelfth ribs the upward and downward 

 movements are but slight, while the forward and backward move- 

 ments are relatively free, owing to the absence of the costo-transverse 

 articulation. 



COSTAL CARTILAGE WITH THE RIB. The end of the rib is hollowed Rib and 

 to receive the costal cartilage, and the two are directly united. The cartilage, 

 periosteum of the rib is continued into the perichondrium of the 

 cartilage. 



CHOXDRO-STERXAL ARTICULATIONS will now be examined in the costal car- 

 portion of sternum that had previously been put aside, and in what tilages with 

 , _ . _, .. n i -i i the sternum, 



remains on the body. The cartilages of the true ribs, except the 



first, are articulated to the sternum by synovial joints. The 

 extremity of each cartilage is received into a depression on the side 

 of the sternum, and is fixed by a surrounding capsule. In front 

 and behind the capsule is thickened by radiating fibres, which are 

 described as anterior and posterior ligaments. 



In the joint of the second cartilage there is an interarticular Second cur- 

 tilage has a 

 double joint. 



