SHOULDER GIRDLE AND ANTERIOR LIMB 509 
TABLE 5 
Showing the results following the removal of the mesoderm within the area a-e X 4-8 
(text fig. 1) 
CONDITION OF THE GIRDLE AND THE EXTREMITY 
INDIVIDUAL AGE 
ease Scapula Procoracoid Coracoid Humerus 
days 
Ext. Gr. C. 4.] 20 present | present absent | rudimentary | present 
BixtenGie Cee 9) e020 present | present absent | rudimentary | present 
dete (Caos (Cle 1835) 20) present | present absent | absent present 
Ext. Gr. €. 19.) 20 present | present absent | absent present 
xt. Gr. C2205) 20 present | present absent | absent present 
The development of a rudimentary coracoid in cases 4 and 9 is no doubt due 
to incomplete removal of the ventral zone rudiment. 
The dorsal zone in these cases ended blindly at the point where 
the humerus began and was ankylosed with it. Shoulder move- 
ments in most of the cases were very slight or entirely wanting. 
In complete absence of the ventral zone, the procoraco-humeral 
and supracoracoideus muscles were also lacking, their rudiments 
having been removed with those of the cartilaginous elements. 
The pectoral muscles, however, were present and followed their 
normal course. 
In other cases following the extirpation of this region the 
function of the limbs was more normal. It was found when 
these larvae were sectioned that, in addition to an imperfectly 
formed glenoid cavity, a small process of cartilage extended ven- 
tral to the proximal end of the humerus which could be identi- 
fied as a very rudimentary coracoid. A short supracoracoideus 
muscle connected this fragmentary coracoid with the humerus. 
No procoracoid element could be distinguished. 
The development of the rudimentary coracoid in these cases 
is evidence of incomplete removal of the entire rudiment of the 
ventral zone. Such cases, while they must be regarded in one 
sense as unsuccessful, have nevertheless an important bearing 
on the question of totipotency of the girdle-forming tissue. If the 
unremoved cells which formed this rudimentary coracoid were 
equipotential, then restitution of the entire ventral zone would 
be expected. This not being the case, it must be said that what 
THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 25, NO. 2 
