SHOULDER GIRDLE AND ANTERIOR LIMB SH ilell 
sharply marked off from each other, thus suggesting the possi- 
bility of their being a single anlage. 
While more or less definite defects in the girdle have resulted 
from the extirpation of regional areas hitherto designated, the 
girdle defects following the removal of either the anterior or pos- 
terior half of the limb dise have not been so definite nor con- 
stant in character. The few specimens used in this study were 
given over by Dr. Harrison, who removed from the embryos the 
anterior and posterior halves of the limb dise in connection with 
his experimental study of the equipotentiality of the limb. 
Three cases were studied in which the anteriorhalf of the disc 
had been removed. In cases Rem. E. 22 and 23, preserved 
forty-six and eighteen days, respectively, after the operation and 
in each of which the limb had developed normally, the only de- 
fect in the girdle consisted in the absence of the procoracoid. 
In case H. R. E. 11—(twenty-six days) in which the limb con- 
sisted of nothing more than a nodule of undifferentiated mesen- 
chyme cells, there was complete absence of the girdle. This 
case bears no significance with regard to localization, since ordi- 
narily after the removal of the entire limb disc, the suprascapula, 
procoracoid, and the coracoid develop (Exp. A 4 and table 4). 
The only point of interest that this case offered was the fact that 
in the absence of skeletal differentiation, two of the shoulder mus- 
cles were differentiated, these being the trapezius and the pectoral. 
Three cases were studied in which the posterior half of the 
limb disc had been removed. Case Rem. EH. 12 (twenty-six days) 
with normally developed extremity showed considerable defects 
in the ventral zone of the girdle. The procoracoid was entirely 
wanting, while the coracoid was greatly reduced in size. The dor- 
sal zone was normal. In case H. R. E. 12—(twenty-six days) 
with defective hand, there was no procoracoid. The coracoid, 
while being normal in length, was somewhat reduced in width. 
The dorsal zone was also poorly developed. In H. R. E. 9— 
(twenty-six days) in which no limb had developed, all parts of 
the girdle were present although somewhat atypical in shape. 
The most pronounced abnormality consisted of a distinct ex- 
chondrosis from the posterior border of the suprascapula. 
