160 



SPECIAL ANATOMY OF THE SKELETON 



attached to the sternum and becomes the ensiform process. The remaining part acquires 

 attachment to the eighth cartilage. These two bars fuse with each other along the middle line, 

 and the bone, including the ensiform appendix, is usually developed from six centres, one for 



the first piece or manubrium, four for the second 

 piece or gladiolus, and one for the ensiform appendix. 

 Up to the middle of fetal 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. 125): In 

 the manubrium and first piece of the gladiolus, during 

 the sixth month; in the second and third pieces of the 

 gladiolus between the seventh and ninth months; 

 the fourth piece of the gladiolus ossifies toward the 

 latter part of the first year; the ensiform process 

 ossifies between the fifth and eighteenth years. The 

 centres appear in the upper part of each segment and 

 proceed gradually downward. To these may be added 

 the occasional existence, as described by Breschet, of 

 two episternal centres, w r hich make their appearance 

 one on each side of the presternal notch. They 

 are probably vestiges of the episternal bone of the 

 monotremata and lizards. It occasionally happens 

 that some of the segments are formed from more than 



none cetre, the number and position of which vary (Fig. 127). 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; 1 the second piece has seldom more than one; the 



FIG. 124. Showing ventral ends of the 

 upper seven (cartilaginous) ribs fused to 

 form a pair of longitudinal sternal bars. 

 ( Rauber-Kopsch.) 



Time 



of 

 appearance 



1 for manubrium 



\6th month 

 21 



4 for gladiolus { [ 7th month 



5 1st year after birth 



FIG. 125. Development of the sternum from six centres. 

 Time of appearance. 



for first piece, two or more centres. 



for second piece, visually one. 

 for third "1 



for fourth } 2, placed laterally, 

 for fifth \ 



Rarely unite, 

 except in old age. 



Between puberty 

 and the 25th year. 



Soon after puberty. 



Partly cartilaginous ft 

 advanced life. 



FIG. 126. Time of union of 

 sternum. 



Arrest of development 

 of lateral pieces, producing 



-Sternal fissure, and 

 .Sternal foramen. 



FIG. 127. Peculiarities in number of centres of sternum. FIG. 128. Peculiarities in mode of union of sternum. 

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



