EXPERIMENTS ON THE FORE LIMB OF AMBLYSTOMA 429 
e 
A larva killed fifteen days after operation (R. E. 129-, fig. 11) 
shows traces of digits and the segregation of some of the skeletal 
elements, though no marked differentiation of tissues. Mi- 
toses are still very numerous and the blood vessels within the 
limb are unusually large. It is odd that there is as yet no trace 
of the shoulder girdle, which is already well developed on the 
normal side. In normal limbs of the size of the regenerating 
one in this specimen, the girdle can be readily made out. 
The shoulder girdle in the absence of the limb 
In cases where the free limb does not regenerate there is a 
partial development of the shoulder girdle. This is shown in 
every case that has been examined, confirming Braus’s obser- 
vations on the Anura. 
Some of these cases have been studied in serial sections and 
others in total preparations of the shoulder region (figs. 12 and 
13). The cartilaginous elements found are a) the coracoid 
(COR), which has the same general shape and position as the 
normal, but is not so large; b) a small nodule, dorsal to the cora- 
coid at the point where the humerus would normally articu- 
late, representing the procoracoid (P. COR), and c) a rod-shaped 
element, external to the pronephros, which is entirely separate 
from the rest of the girdle and which may be identified with 
the suprascapula (GS. SC). The scapula is absent. The ven- 
tral trunk musculature is approximately normal, though thinner 
in ‘the girdle region, and usually it is partly interrupted. A 
distinct band of musele running from the ventral end of the 
suprascapula dorsally and anteriorly just under the epidermis 
is to be identified with the m. trapezius, though in the normal 
girdle this muscle is attached further ventrally. The condi- 
tions found change with the age of the specimen. 
In a ease preserved eighteen days after extirpation of the 
limb bud (E. E. 61) there are only two small nodules of carti- 
lage, or rather precartilage, present. One is at or slightly ven- 
tral to the level of the normal shoulder joint and represents 
the coracoid, and the other is between the muscle plates and 
skin at the level of the notochord, opposite the dorsal extremity 
THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 25, NO. 2 
