192 THE SKELETON. 



has been likened to an ancient sword: the upper piece, representing the handle, 

 is termed the manubrium; the middle and largest piece, which represents the 

 chief part of the blade, is termed the gladiolus ; and the inferior piece, which 

 is likened to the point of the sword, is termed the ensiform or xiphoid appendix. 

 In its natural position, its inclination is oblique from above, downwards, and 

 forwards. It is flattened in front, concave behind, broad above, becoming nar- 

 rowed 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, 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 down- 

 wards, 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 interclavicular notch; and on each side, an oval 

 articular surface, directed upwards, backwards, and outwards, 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 articula- 

 tion with the second portion of the bone. The lateral borders are marked above 

 by an articular 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 downwards and inwards. 



The Second Piece of the sternum, or Gladiolus, considerably longer, narrower, 

 and thinner than the first piece, is broader below than above. Its anterior sur- 

 face is nearly .flat, directed upwards and forwards, and marked by three trans- 

 verse 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 backwards. 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 articula- 

 tion 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 appen- 

 dix, forms a notch for the cartilage of the seventh rib. These articular depres- 

 sions .are separated by a series of curved inter-articular intervals, which diminish 

 in length from above downwards, and correspond to the intercostal spaces. 

 Most of the cartilages belonging to the true ribs, as will be seen from the fore- 

 going description, articulate with the sternum at the line of junction of two of 

 its primitive component segments. 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. 



