THE SKELETON 47 



In the adults of the higher quadrupedal Mammals, the episteruum 

 is possibly for the most part represented by a couple of cartilaginous 

 tracts, approximated to the sternal ends 

 of the clavicles (es., Fig. 30); and its 

 body (es!, Fig. 29), so far as is known, 

 appears to become reduced, and either 

 closely apposed to or fused with the 

 anterior end of the sternum. 



The following information concern- 

 ing the human episternum is largely 

 drawn from the admirable work of Euge. 



In an early embryonic stage, when 

 the cartilaginous " sternal bands " have, 

 not yet united along their whole length, 

 two independent masses, which soon be- FIG. 29. EPISTERXUM OF AN 

 come cartilaginous, appear at the upper G^tte. 

 end of the still forked manubrium sterni. *<> sternum; es'., central portion 



, \ce of the episteruum ; es. , lateral 



At a later stage they fuse to form a portion of the same ; d, cia- 

 single cartilaginous tract, which gradu- vicle ; r - c -> costal ribs - ( The 



. , --IPI. .LIP! ti ure was constructed from 



ally interposes itself between the forks two consecutive horizontal 

 of the manubrium, until finally only sections.) 

 the proximal surface of the cartilage projects from that struc- 

 ture. As the two sternal ridges fuse completely, the boundary 

 lines between the episternal cartilages and the manubrium 

 become more and more indistinct, and finally altogether 

 disappear, the former structure becoming incorporated in the 

 latter. The manubrium of Man is thus a compound of two 

 separate structures, one of which is certainly costal and 

 derivative of the first pair of ribs. The homology of the other, 

 i.e. of the suprasternal portion, cannot yet be decided with any 

 certainty. There can be no doubt that we have in it the last 

 vestiges of a skeletal structure, but whether they are those of a 

 seventh pair of cervical ribs which once reached the manubrium, 

 or of the central portion of the episternum of the Monotremes 

 and lower Mammalia, must for the present remain undecided. If 

 the latter supposition should prove correct, it would point to 

 the originally paired nature of the Mammalian episternum, and 

 support Gotte's view of its origin from the median ends of 

 the clavicles. 



Brechet's cartilages, or bones, which occasionally appear at 

 the antero-internal border of the sterno-clavicular articulation, 

 and either become closely applied to the sternum or united with 



