STERNUM. 



193 



The Third Piece of the 

 sternum, the Ensiform or 

 Xiphoid Appendix, is the 

 smallest of the three; it is 

 thin and elongated in form, 

 cartilaginous in structure in 

 youth, but more or less os- 

 sified at its upper part in the 

 adult. Its anterior surface 

 affords attachment to the 

 costo-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 is continuous with the 

 lower end of the gladiolus; 

 below, by its pointed ex- 

 tremity, it gives attachment 

 to the linea alba, and at each, 

 superior angle presents a fa- 

 cet for the lower half of the 

 cartilage of the seventh rib. 

 This portion of the sternum 

 is very various in appear 

 ance, being sometimes point- 

 ed, broad, and thin, some- 

 times bifid, or perforated by 

 a round hole, occasionally 

 curved, or deflected conside- 

 rably to one or the other 

 side. 



Structure. The bone is 

 composed of delicate cancel- 

 lated texture, covered by a 

 thin layer of compact tissue, 

 which is thickest in the 

 manubrium, between the ar- 

 ticular facets for the clavi- 

 cles. 



Development. The ster- 

 num, including the ensiform 

 appendix, is developed by 

 six centres; one for the first 

 piece, or manubrium, four 

 for the second piece or gla- 

 diolus, and one for the en- 

 siform appendix. Up to the 

 middle of fcetal life, the ster- 

 num is entirely cartilaginous, 

 and when ossification takes 

 place, the ossific granules 

 are deposited in the middle 

 of the intervals between the 

 articular depressions for the 

 13 



Fig. 138. Development of the Sternum, by Six Centres. 



'T Iff piece fS-ti mo.faSa.l' 



5 . lf.u-a,fla 



1 ^ * r . 



j * 



Fig. 139. 



rarely u-nite . 

 J except inold a c/e 



35-1,0. 



'year 

 I soon after puberty 



fttrtly cartilaginous in 

 advanced life 



Fig. 140. Peculiarities. 



for H? piece Zar laorc fcntre* 

 %.". -piece. 



In 

 nu fit 6 e/<r of 



Centres ^ 3]^ ^ \ *J>U*cd laterally 



Fig. 141. 



And in 

 Mode of 



Union, 



of 



trf latera/l pieces producing 

 Sternal fissure & 



-Sternal fora nun 



