THE STERNUM. 



97 



border, curved and irregular, is slightly everted. Articu- 

 lating with the sides of the body are the greater cornua, 

 and attached to the body by a plate of cartilage are two 

 epiphyseal cartilages, the lesser cornua. The greater 

 cornua are somewhat flattened, taper from before back- 

 ward, and terminate in clubbed extremities, which give 

 attachment to the thyro-hyoid ligaments. The articula- 

 tion between these processes and the body rarely persists 

 beyond the fiftieth year. The lesser processes project 

 slightly upward and backward from the body just above 

 the articular surfaces for the greater cornua ; they are 

 short, conical processes, 

 which afford attachment 

 to the stylo-hyoid liga- 

 ments. The hyoid is an 

 eminently elastic bone, 

 consisting of equal por- 

 tions of organic and 

 earthy matter. The cor- 

 nua are largely cartilagi- 

 nous in character. This bone develops by five centres, 

 one for the body and one for each cornu. 



THE THORAX. 



The thorax is formed by the sternum and costal 

 cartilages in front, the bodies of the vertebrae behind, 

 laterally by the ribs. It is an osseo-cartilaginous struc- 

 ture, flattened antero-posteriorly, is highly elastic, and 

 susceptible of an increase in all its diameters by the 

 action of the muscles of respiration. It contains the 

 heart, lungs, great vessels and nerves. 



THE STERNUM. 



The sternum, or breast-bone, is a flat bone situated 

 in the median line, articulating with the clavicle above 



FIG. 44. THE HYOID BONE. 



