42, M. L. Shorey 
attempting to detach it the surrounding tissues were somewhat 
torn. Still it was possible to identify the muscles and trace the 
course of the nerves. 
Not all the muscles are yet clearly defined, but of those which 
are, the pectoralis secundus, the subscapularis and latissimus 
dorsi were entirely extirpated by the operation. ‘The humerus 
and coracoid are abnormal and the scapula completely destroyed. 
The peripheral distribution of the nerves is shown in Fig. 36. 
Measurements of the nerve trunks show an average loss of 
314 per cent in width. ‘The ganglia are not noticeably affected. 
The dorso-ventral diameter of the spinal cord and the lateral 
diameter of the ventral portion are less on the operated side, 
but the posterior horn exhibits no change. ‘The boundaries of the 
ventral horn on the operated side are, in many sections, less 
sharply outlined, and exact measurements are difficult to obtain, 
but a very conservative estimate of the average loss in width is 
18 per cent. As in Experiment 179 the distance from the neural 
canal to the motor nucleus is sometimes greater on the operated 
side, and as this is the case where the boundaries are least definite, 
I again assume it to be possible that certain neuroblasts were 
formed which did not reach their normal location in the ventral 
horn. A section of the spinal cord at the level of the 15th nerve 
is shown in Fig. 20. 
Experiment 404. Of specimens preserved when five days old, 
or two days after the removal of the wing bud, I shall again con- 
fine myself to a detailed description of a single embryo, since others 
of the same age differ only in the extent of the injury. At this 
period the bones and muscles are not yet sufficiently differentiated 
to be identified, so that it is impossible to say exactly what struc- 
tures have been destroyed, but there is only the slightest promi- 
nence in the region of the wing on the operated side. Fig. g will 
show the stage of development as well as the extent of the injury. 
Fig. 38 shows the peripheral distribution of the nerve fibers. 
The branching on the operated side is decidedly less extensive, 
yet I am unable to demonstrate more than 4 per cent of loss in 
the average width of the nerve trunks, and I do not feel certain that 
this is not within the limits of error in measuring these with the 
