SHOULDER GIRDLE AND ANTERIOR LIMB 501 
2. NORMAL ANATOMY 
In order that the experiments may be more fully understood, 
a description of the normal girdle will first be given. Chondri- 
fication of the girdle is practically complete in a larva about 
twenty days after the closure of the medullary folds. The girdle 
then consists of a cartilaginous structure lying within the body 
wall and extending from the lateral aspect of the third myo- 
tome almost to the mid-ventral line (fig. 6). It is made up 
of the following components: a) the suprascapula, which con- 
sists of a rod-shaped element lying external to the pronephros 
and constituting the greater portion of the dorsal zone (fig. 23, 
s.sc); b) the scapula, which lies just dorsal and anterior to the 
glenoid cavity and which, in the cartilaginous state, is continu- 
ous with the suprascapula (fig. 28, sc); ¢) the procoracoid lying 
immediately anterior and slightly ventral to the glenoid cavity 
(fig. 23, p.cor), and d) the coracoid, a relatively broad expanse 
of cartilage, constituting nearly the entire ventral zone of the 
girdle and reaching close to the mid-ventral line (fig. 7, cor. and 
fig. 23, cor.). The scapula, procoracoid, and coracoid are con- 
tinuous proximally and enter into the formation of the glenoid 
cavity which receives the head of the humerus (fig. 23, ge). 
Chondrification 
Chondrification of the girdle proceeds gradually from the cen- 
tral portion towards the periphery. ‘There are three centers, one 
for the scapula, one for the coracoid, and one for the procoracoid. 
The center for the scapula is first to appear. This is followed by 
the center for the coracoid and finally by the procoracoid center. 
This was found by Wiedersheim (’89) to be the case with Triton, 
Siredon, and Salamandra. The same observation was also made 
by Braus (09) on Bombinator. 
The union of these three centers completes the chondrification 
of the central portion of the girdle. The suprascapula has no 
separate center and chondrification of this element proceeds 
gradually from the region of the scapula in a dorsal direction. 
