OSTEOLOGY AND SYNDESMOLOGY. 27 



which, having attached to it the clavicle and the first and half of the second 

 rib, is known as the manvhrium. The middle piece, or yladiolus, presents 

 six notches on each side. The inferior extremity is known as the xiphoid 

 2)rocess: this is thin and cartilaginous, expanded towards the extremity, 

 where it is rounded, pointed, or bifid. There is frequently a perforation 

 in the centre. 



The ribs, costce {pi. 122, fiys. 3, 4, and 5), are twelve in number on each 

 side. They extend in an arched manner from the vertebraj towards the 

 sternum, to which the seven superior pairs are attached by separate carti- 

 lages. These are the true or vertebrosternal ribs. The five inferior pairs 

 do not reach the sternum, but are connected anteriorly with each other and 

 to the cartilages of the last true rib; they are known as /aZse or vertehro-costal 

 or asternal ribs. The two last pairs are sometimes Q,ö\\e(\. floating or vertebral 

 ribs. The length of the ribs gradually increases from the first to the eighth 

 pairs, then diminishes again to the last. The external surface of the body 

 is smooth and convex ; the internal is concave. The upper border is round 

 and smooth, and gives attachment to the intercostal muscles. The inferior 

 border is thin and marked with a groove on the inner side ; its edges give 

 attachment to the intercostal muscles, while in the groove are lodged the 

 intercostal vessels. 



The posterior end of a rib presents a head, neck, and tuberosity. The 

 head is round and divided by a ridge into two articular surfaces, the inferior 

 of which is the larger ; these are received into the depressions in the dorsal 

 vertebrae : an interarticular ligament is attached to the middle ridge. The 

 head is supported by the neck, which lies in front of the transverse process, 

 to which its posterior surface is connected by a ligament. Beyond or exter- 

 nal to the neck is the tubercle, which looks backwards and downwards, and 

 is divided into two portions. Of these, the internal is smooth for articulation 

 with the transverse process of the inferior of the two vertebree, to whose 

 bodies the head of the rib is connected. The external is rough for the 

 insertion of a ligament. 



The cartilages which connect the ribs with the sternum must be con- 

 sidered as part of the skeleton. They are twelve in number on each side, 

 and of nearly the same form as the shafts of the ribs. They serve to give 

 great strength and elasticit}^ to the thorax, and permit the free play required 

 by the lungs and heart. 



* 



B. Articidations and Ligaments of tlie Thorax. 



The head of each rib is secured to the vertebrae by an anterior or stellate 

 ligament, an interarticular, and two synovial membranes. The tubercle is 

 secured in its socket by a synovial membrane, and by an external posterior 

 and an anterior or internal costo-transverse ligament. 



The capsular^ stellate^ or anterior ligament {pi. 125, fig. 1 '') arises from the 

 front of the head of the rib, and thence extends over the two synovial 

 membranes in a radiated manner, and is inserted by three bands, one into 

 the sides of the vertebrae above and below, and the third into the inter- 

 vertebral substance. The interarticidar ligament {fig. 1') arises from the 



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