,J56 



HUMAN ANATOMY. 



lower edge. The first and second pieces of the body are about equal in length ; the 

 third is shorter, and the fourth still more so ; hence the fifth, sixth, and seventh 

 cartilages end very close together, especially the two last. 



The ensiform cartilage,' or xiphoid process, more or less bony in middle 

 life, is a flat plate with a rounded end, not rarely bifid. It is fastened to the lower 

 end of the body in such a way that their posterior surfaces are continuous, but that 

 the ensiform, being thinner, is overlapped by the ends of the seventh cartilages ; its 

 front is therefore at a deeper level than that of the body. The size and shape of 

 the ensiform cartilage are very uncertain ; usually the tip projects somewhat forward. 



DifTerences due to Sex. — The body of the male sternum is both absolutely 

 and relatively longer than that of the female. This is in accordance with the greater 

 development of the male thorax. The following table gives the actual size, accord- 

 ing to the writer^ and to Strauch.^ 



DWIGHT. 

 Men. Women. 



Centimetres. Centimetres. 



Manubrium 5.37 4.94 



Body 11.04 9-19 



Total 16.41 14-13 



16.063 



14-115 



Fig. 180. 



Hyrtl gave a rule for determining the sex, that the manubrium of the female 

 exceeds half the length of the body, while the latter in the male is at least twice as 



long as the manubrium. A study of 342 sterna, of 

 which 222 were male and 120 female, confirmed Hyrtl's 

 law for the mean ; since, however, approximately forty 

 per cent, of the cases were exceptions, it is clearly 

 worthless to determine the sex in any given case. 

 Probably the law would be correct if we had to do 

 only with well-formed sterna, but the body varies 

 greatlv. It is easy to recognize a typical male or 

 female sternum. The former has a long, regular body, 

 the lower pieces of which are well developed, sepa- 

 rating the lower cartilages of the true ribs. The latter 

 has a shorter and relatively broader body, the lower 

 parts of which are poorly developed, so that the carti- 

 lages are near together, and the seventh ones of the two 

 sides almost, or quite, meet below the body in fiont of 

 the base of the ensiform. 



Variations. — The very rare cases of fissure of 

 the sternum, and the not uncommon ones of perfora- 

 tion in the median line, represent different degrees of 

 arrest of development. The lower half of the sternum 

 is sometimes imperfectly developed. We have de- 

 scribed a case in a negress in which there was but little 

 and irregular ossification below the fourth costal carti- 

 lage. A very rare anomaly is that of the manubrium 

 being prolonged to the insertion of the third costal 

 cartilages, as occurs usually in the gibbons and occa- 

 sionally in other anthropoid apes. 



The suprasternal bones, very rarely seen in the 

 adult, are a pair of rounded bones compressed later- 

 ally, about the size of peas, placed on the top of the 

 manubrium at the posterior border just internal to the sterno-clavicular joint. They 

 are presumably the tops of the lateral cartilaginous strips forming the sternum, in 

 which they are normally lost. They are regarded as representing the episternum 

 of lower vertebrates. 



^Journal of Anatomy and Physiology, vol. x.xiv., 1890. '^ Inaug. Disser., Dorpat, 1881. 



' Processus xipboideus. 



Foramen 



Sternum, showing foramen due to im- 

 perfect union of lateral parts. 



