Bones of the Thorax. 



Capitulum 

 costae 



Crista capituli 



Tubercnlum costae 

 Corpus costae 



T 



Sulcus costae 



Angulus costae 



97. Seventh rib of right side, costa VII, from within. 



The twelve costae (ribs) (see also Figs. 105 107) are thin, partly bony, partly carti- 

 laginous masses which go out on each side from the lateral surfaces of the thoracic vertebrae 

 and which, forming an arch which is convex lateral ward, help to bound the thoracic cavity. 

 Each thoracic vertebra corresponds to a pair of ribs ; they are numbered from above downward. 

 The upper seven (sometimes eight) pairs of ribs are fastened directly to the sternum 

 in front near the median plane and are distinguished as costae verae (true ribs) from the 

 lower five (sometimes four) pairs of ribs, the costae spuriae (false ribs), which are indirectly 

 connected with the sternum or else end free. 



Each rib consists of a longer posterior bony portion, os costale, and a shorter, anterior, 

 cartilaginous portion, the cartilago costalis. 



Each os costale is somewhat expanded at its vertebral end so as to form the capitulnm 

 costae (head of the rib) ; this possesses a small fades articularis capituli costae, covered over 

 with cartilage, which is divided, on the ribs from the second to the tenth, by a transverse 

 ridge, crista capituli, into an upper smaller and a lower larger surface. By means of these joint 

 surfaces the heads of the ribs articulate with the foveae costales of the bodies of the vertebrae. 

 The portion of the bone adjoining the capitulnm is somewhat narrowed, collum costae (neck 

 of the rib), on the upper ribs more distinctly than on the lower; the neck presents on its 

 upper margin a longitudinal ridge, crista colli costae, which is continued lateralward upon the 

 shaft and is absent only from the first and the last ribs; at its lateral extremity a small 

 nodule, tuberculum costae, projects backward and downward; this possesses a small fades 

 articularis tuberculi costae, covered with cartilage, for articulation with the fovea costalis 

 transversalis of the corresponding vertebra; it is largest on the first ribs and is absent, along 

 with the joint surfaces, on the (tenth) eleventh and twelfth ribs. 



