THE STERNUM. 



127 



appendix. Up to the middle of foatal life the sternum 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 costal cartilages, in the following 

 order (Fig. 81): In the first piece, between the fifth and sixth months; in the 

 second and third, between the sixth and seventh months ; in the fourth piece, at 

 the ninth month ; in the fifth, within the first year or between the first and second 

 years after birth ; and in the ensiform appendix, between the second and the seven- 

 teenth or eighteenth years, by a single centre which makes its appearance at the 

 upper part and proceeds gradually downward. To these may be added the 



for first piece, two or more centres. 



for second piece, usually one. 

 for third ] 



for fourth } 2, placed laterally, 

 for fifth J 



FIG. 81. Development of the sternum by six 

 centres. Time of appearance. 



Arrest of development 

 of lateral pieces, producing 



-Sternal fissure, and 

 -Sternal foramen. 



FIG. 82. Time of union of sternum. 



occasional existence, as described by Breschet, of two small episternal centres, 

 which make their appearance one on each side of the presternal notch. They are 



1 for 1st piece \ 6th fc f tl 

 or manubnum j 



4 for 2nd piece 

 or gladiolus 



6-7th month. 



4 9th month. 



5 1st year after 



'birth. 



18th year. 



1 for ensiform 



cartilage 



FIG. 83. Peculiarities in number of centres of 

 sternum. 



Rarely unite, 

 j except in old age. 



Between puberty 

 and the 25ih year. 



Soon after puberty. 



Partly cartilaginous to 

 advanced life. 



FIG. 84. Peculiarities in mode 

 of union of sternum. 



probably vestiges of the episternal bone of the monotremata and lizards. It 

 occasionally happens that some of the segments are formed from more than one 

 centre, the number and position of which vary (Fig. 83). Thus, the first piece 

 may have two, three, or even six centres. When two are present, they are 

 generally situated one above the other, the upper one being the larger ;* the second 

 piece has seldom more than one ; the thii'd, fourth, and fifth pieces are often formed 

 from two centres placed laterally, the irregular union of which will serve to explain 

 the occasional occurrence of the sternal foramen (Fig. 84), or of the vertical fissure 

 which occasionally intersects this part of the bone, and which is further explained 

 by the manner in which the cartilaginous matrix, in which ossification takes place, 

 is formed. Union of the various centres of the gladiolus commences about 

 puberty, from below, and proceeds upward, so that ,by the age of twenty- 



'Sir George Humphry states that this is "probably the more complete condition." 



