THE STERNUM. 229 



narrowed at the point where the first and second pieces are connected, after which 

 it again widens a little, and is pointed at its extremity. Its average length in the 

 adult is six inches, being rather longer in the male than in the female. 



The First Piece of the sternum, or Manubrium ( pre-stertium\ is of a somewhat 

 triangular form, broad and thick above, narrow below at its junction with the 

 middle piece. Its anterior surface, convex from side to side, concave from above 

 downward, is smooth, and affords attachment on each side to the Pectoralis major 

 and sternal origin of the Sterno-cleido-mastoid muscle. In well-marked bones the 

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

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

 and Sterno-thyroid muscles. The superior border, the thickest, presents at its 

 centre the pre-sternal notch ; and on each side an oval articular surface, directed 

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

 clavicle. The inferior border presents an oval, rough surface, covered in the recent 

 state with a thin layer of cartilage, for articulation with the second portion of the 

 bone. The lateral borders are 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 middle portion of the bone, forms a notch for the reception of the 

 costal cartilage of the second rib. These articular surfaces are separated by a 

 narrow, curved edge, which slopes from above downward and inward. 



The Second Piece of the sternum, or Gladiolus (rneso-sternuni), considerably 

 longer, narrower, and thinner than the first piece, is broader below than above. 

 Its anten'r surface is nearly flat, directed upward and forward, and marked by 

 three transverse lines which cross the bone opposite the third, fourth, and fifth 

 articular depressions. These lines are produced by the union of the four separate 

 pieces of which this part of the bone consists at an early period of life. At the 

 junction of the third and fourth pieces is occasionally seen an orifice, the sternal 

 foramen : it varies in size and form in different individuals, and pierces the bone 

 from before backward. This surface affords attachment on each side to the 

 sternal origin of the Pectoralis major. The posterior surface, slightly concave, is 

 also marked by three transverse lines, but they are less distinct than those in 

 front : this surface affords attachment below, on each side, to the Triangularis 

 sterni muscle, and occasionally presents the posterior opening of the sternal 

 foramen. The superior border presents an oval surface for articulation with the 

 manubrium. The inferior border is narrow, and articulates with the ensiform 

 appendix. Each lateral border presents, at each superior angle, a small facet, 

 which, with a similar facet on the manubrium, forms a cavity for the cartilage of 

 the second rib ; the four succeeding angular depressions receive the cartilages of 

 the third, fourth, fifth, and sixth ribs ; whilst each inferior angle presents a small 

 facet, which, with a corresponding one on the ensiform appendix, forms a notch 

 for the cartilage of the seventh rib. These articular depressions are separated by 

 a series of curved interarticular intervals, which diminish in length from above 

 downward, and correspond to the intercostal spaces. Most of the cartilages 

 belonging to the true ribs, as will be seen from the foregoing description, articulate 

 with the sternum at the line of junction of two of its primitive component seg- 

 lents. This is well seen in many of the lower animals, where the separate parts 

 of the bone remain ununited longer than in man. In this respect a striking 

 analogy exists between the mode of connection of the ribs with the vertebral 

 column and the connection of their cartilages with the sternal column. 



The Third Piece of the sternum, the Ensiform or Xiphoid Appendix (meta- 

 sternum), is the smallest of the three; it is thin and elongated in form, cartilagi- 

 nous in structure in youth, but more or less ossified at its upper part in the adult. 

 Its anterior surface affords attachment to the chondro-xiphoid ligament; its 

 posterior surface, to some of the fibres of the Diaphragm and Triangularis sterni 

 muscles ; its lateral borders, to the aponeurosis of the abdominal muscles. Above 

 it articulates with the lower end of the gladiolus, and at each superior angle 

 presents a facet for the lower half of the cartilage of the seventh rib ; below, by 



