THE STERNUM. 



155 



lage, the falling portion becoming always relatively shorter and the rising longer. 

 The last two cartilages continue the line of their ribs, having no rising portion. It 

 is not uncommon to find eight cartilages joining the sternum. Tredgold found this 

 condition in ten per cent, of white men. It is very 

 much more frequent in negroes and in other dark Fig. 179. 



races.' It is said to occur more often on the right side. 



THE STERNUM. 



Clavicular 

 facet 



■.fk^ 



First rib-- 

 cartilage 



m 



MANUBRIUM 



Second  



Third- 



The adult sternum consists of three flat median 

 plates, the two former being bone, the last largely car- 

 tilage, — namely, the presternum or vianiibrium, the 

 me so sternum, gladiolus, or body, and the nietasteriium 

 or ensiform cartilage. 



The manubrium ^ is broad in mammals having 

 clavicles, to which it gives support at the upper angles. 

 In man it is irregularly quadrilateral, with the angles 

 cut off, broad above, narrower below, the greatest 

 breadth equalling or exceeding the length. It is con- 

 cave behind, but in front it is convex from side to side 

 and slightly concave from above down. The upper 

 border is concave in the middle, forming the bottom 

 of the interclavicular notch."^ On each side of this, in 

 the place of a corner, is a concavity for the sternal end 

 of the clavicle. This depression * is more on the top 

 than on the side of the sternum, and usually encroaches 

 more on the back of the bone. It is concave from 

 within outward and may, or may not, be slightly con- 

 cave from before backward. The facet is coated with 

 articular cartilage. Just below the joint, the side of 

 the manubrium projects outward to meet the cartilage 



of the first rib. This is the widest part of the first 11/''>A1 



piece, the border then slanting inward to the lower 

 angle, which also is cut off by a notch for the second 



costal cartilage, which is received between it and the /IC^I 



body. The lower border, separated from the meso- mJ^A 



sternum by fibro-cartilage, projects a little forward into 

 a transverse ridge, always to be felt in life, which in- 

 dicates the level of the second costal cartilage. 



The oblong body, or gladiolus,* ossifying origi- 

 nally in four pieces, one above another, varies con- 

 siderably in shape. It is generally slightly concave 

 behind and nearly plane in front, but it may be convex 

 or even concave. The greatest breadth is below the 

 middle, whence the borders slant inward to the lower 

 end, the narrowest part, where it joins the ensiform 

 cartilage. The sides of the body present alternately 

 smooth concavities opposite the spaces between the 

 costal cartilages and articular facets for the latter. To 

 understand the position of these articular facets, we 

 must recall the composition of the mesosternum as 

 consisting of four pieces. The second cartilage reaches 

 the junction of the manubrium and the body ; the third, 

 that of the first and second pieces of the body ; the 

 fourth, that of the second and third pieces ; the fifth, that of the third and fourth 

 pieces. The two rem.aining sternal ribs send their cartilages to this fourth piece of 

 the body ; the sixth to the side, and the seventh to the lower angle, or even the 

 1 Journal of Anatomy and Physiolog>', vol. xxxi, 1897. Lamb : Nature, 1888. 



BODY 



Fourth- 



m 



H. 



Fifth- 



Sixth- 



Seventh- 



ENSIFORM 

 CARTILAGE 



Right side of sternum. 



- Man<ibrium sterni. ^ Incisura jugularis. * Incisura clavicul 



laris. '' Corpus sterni. 



