THORACIC JOINTS 113 



without any synovial membrane, or other material, intervening. The 

 second costal cartilage is usually separated from the sternum by two 

 synovial cavities, between which an interarticular ligament is developed. 

 In the case of the other joints it is more common to find a single synovial 

 cavity and no interarticular ligament. There is, however, considerable 

 variety in these articulations, and a synovial membrane is very frequently 

 wanting altogether in the sterno-chondral joint of the seventh costal 

 cartilage. 



With the exception of the first, which is a synchondrosis, 

 the sterno-chondral joints belong to the diarthrodial variety. 

 They are provided with anterior and posterior ligaments, and 

 also, in those cases where the joint presents a double synovial 

 cavity, with an interarticular ligament. 



Anterior and posterior sterna-costal radiate ligaments. These 

 are strong, flattened bands of fibres which radiate from the 

 extremities of the rib-cartilages and blend with the periosteum 

 on the anterior and posterior surfaces of the sternum. The 

 interarticular ligaments are feeble bands which pass from the 

 tips of the rib-cartilages to the sternum, and divide the articu- 

 lations in which they exist into an upper and a lower com- 

 partment, each of which is lined with a synovial stratum. 



Inter-chondral Articulations. Interchondral joints are 

 formed between the adjacent margins of the ribs from the 

 sixth to the tenth. The joint cavities are surrounded by 

 ordinary capsular ligaments, each of which is lined internally 

 with a synovial stratum ; they are, therefore, diarthrodial 

 joints. 



Costo-vertebral Articulations. The costo-vertebral joints 

 are separable into two groups, capitular and costo-transverse. 



The capitular articulations are the joints between the heads 

 of the ribs and the bodies of the vertebrae and the interverte- 

 bral fibre-cartilages ; they are diarthrodial joints. With the 

 exceptions of the first and the last three ribs, the head of 

 every rib articulates with the bodies of two adjacent vertebrae 

 and the intervening intervertebral fibro-cartilage, and it is 

 connected with them by an articular capsule and an inter- 

 articular ligament. The interarticular ligament connects the 

 intervertebral fibro-cartilage with the ridge which separates 

 the two facets on the head of the rib. It is united, anteriorly 

 and posteriorly, with the capsule, and separates the joint cavity 

 into an upper and a lower compartment. The anterior part 

 of the. capsule is specialised into three radiating bands which 

 form the radiate ligament. The upper and lower bands go 



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