120 



OSTEOLOGY 





behind; broad above, becoming narrowed at the point where the manubrium joins 

 the body, after which it again widens a little to below the middle of the body, 

 and then narrows to its lower extremity. Its average length in the adult is about 

 17 cm., and is rather greater in the male than in the female. 



Manubrium (manubrium sterni). The manubrium is of a somewhat quad- 

 rangular form, broad and thick above, narrow below at its junction with the body. 



Surfaces. Its anterior surface, convex from side to side, concave from above 

 downward, is smooth, and affords attachment on either side to the sternal 

 origins of the Pectoralis major and Sternocleidomastoideus. Sometimes the 

 ridges limiting the attachments of these muscles are very distinct. Its posterior 

 surface, concave and smooth, affords attachment on either side to the Sterno- 

 hyoideus and Sternothyreoideus. 



For 1st 

 '-i- costal 

 ' cartilage 



Sternal 

 angle 



Xiphoid process 



FIG. 116. Posterior surface of sternum. 



Articular surface 

 for clavicle 



Depression for 



Ittt costal cartilage 



Manubrium 



Demifacfts for 2nd costal 

 cartilage 



Facet for 3rd costal cartilage 

 Body 



Facet for Atn costal cartilage 



Facet for 5th costal cartilage 



-Facet for Glh costal cartilage 

 -Facet for 1th costal cartilage 

 Xiphoid process 



FIG. 117. Lateral border of sternum. 



Borders. The superior border is the thickest and presents at its center the jugular 

 or presternal notch ; on either side of the notch is an oval articular surface, directed 

 upward, backward, and lateralward, for articulation with the sternal end of the 

 clavicle. The inferior border, oval and rough, is covered in a fresh state with a 

 thin layer of cartilage, for articulation with the body. The lateral borders are each 

 marked above by a depression for the first costal cartilage, and below by a small 

 facet, which, with a similar facet on the upper angle of the body, forms a notch 

 for the reception of the costal cartilage of the second rib. Between the depression 

 for the first costal cartilage and the demi-facet for the second is a narrow, curved 

 edge, which slopes from above downward and medialward. 



Body (corpus sterni; gladiolus) . The body, considerably longer, narrower, and 

 thinner than the manubrium, attains its greatest breadth close to the lower end. 



Surfaces. Its anterior surface is nearly flat, directed upward and forward, 

 and marked by three transverse ridges which cross the bone opposite the third, 



