TRANSPLANTATION OF LIMBS IN AMBLYSTOMA 127 
ventral surface of the humerus, ventral to the m. anconaeus 
scapularis medialis and medial to the m. brachialis inferior. It 
inserts on the ventral surface of the distal two-fifths of the 
humerus. 
Innervation: by the n. coraco-brachialis (fig. 2, n. cor. br.). 
9. M. anconaeus scapularis medialis. This muscle takes origin 
by means of a long, flat tendon from the glenoid margin of the 
scapula and from the capsule of the shoulder joint. <A portion 
unites with the tendon of the m. latissimus dorsi; the remainder 
passes out on the dorsomedial surface of the humerus, between 
the m. coraco-brachialis and the m. anconaeus humeralis lateralis 
with which it finally unites. It inserts in common with the m. 
anconaeus humeralis lateralis and the m. anconaeus humeralis 
medialis on the olecranon process of the ulna. 
Innervation: through the n. brachialis longus superior. 
According to Fiirbringer some of the deep posterior fibers of 
the m. supracoracoideus in Salamandra leave this muscle, join 
the fibers of the m. brachialis inferior and insert with it on the 
proximal part of the radius and ulna. This muscle he calls the 
m. coraco-radialis proprius. A similar structure in Ambly- 
stoma could not be identified either in the larval or in the adult 
individual. 
C. The brachial plexus 
In the so-called tail-bud stage, the period of development in 
which the experiments reported in this paper were carried out, 
the position and extent of the anterior limb rudiment, as has 
already been shown by Harrison (’15), constitutes a slightly 
thickened region of somatopleural mesoderm lying just ventral 
to the pronephros and extending from the anterior border of 
the third somite to the posterior border of the fifth. The normal 
anterior limb is supplied by a plexus composed of the third, 
fourth, and fifth spinal nerves (fig. 2). The outgrowing nerves 
above enumerated, effecting connection with the limb rudiment 
at a period when it occupies its maximum extent (anterior border 
of the third somite to the posterior border of the fifth) become 
converged into a plexus as a result of concentration of the rudi- 
