THE SKELETON 47 
In the adults of the higher quadrupedal Mammals, the episternum 
is possibly for the most part represented by a couple of cartilaginous 
tracts, approximated to the sternal ends Le 
CS. 
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 Ruge. 
In an early embryonic stage, when 
the cartilaginous “sternal bands” have 
not yet united along their whole length, 
two independent masses, which soon be- Fic. 29.—EprsterNum oF aN 
: . Emspryo More. (After A. 
come cartilaginous, appear at the upper Gitte.) 
end of the still forked manubrium sterni. *., sternum; ¢s’., central portion 
of the episternum ; es.”, lateral 
At a later stage they fuse to form a portion of the same; cl., cla- 
single cartilaginous tract, which gradu- viele; 7.¢., costal ribs. (The 
: . figure 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 appled to the sternum or united with 
