II1O BYRNES. [VoL. XIV. 
myotome-processes, as their subsequent fate has no bearing on 
the question of the origin of the limb-muscles. The details of 
their later development are given in Maurer’s paper on Siredon. 
Simultaneously with the early development of the myotome- 
processes the anterior limbs begin to develop. They originate 
as somatopleuric thickenings formed by an aggregation of 
mesenchyme-like cells around a slight fold of the epithelium bor- 
dering the coelom (PI. X, Fig. 1). H.H. Field has already called 
attention to this fold and its relation to the rudimentary limb. 
The anterior limb-rudiments develop some distance de/ow the 
level of the myotomes; hence, when the myotome-processes 
elongate ventrally they project toward the limbs. During the 
very early stages of development all the cells are so crowded 
with yolk-granules that the line of demarcation between the 
myotome-processes and the rudimentary limbs is often obscured. 
In favorable cases, however, a line of pigment bordering the 
myocoel outlines the extent of the process so that it can be 
followed (Pl. X, Figs. 3, 4). The apparent fusion of the 
myotome-process with the rudimentary limb-mass can often be 
explained as due to the fact that the myotome-processes are cut 
obliquely. Such sections often show no distinct space between 
the myotome-process and the limbs. The true relations be- 
tween the myotome-processes and the anterior limb-rudiments 
in Amblystoma are further obscured by the early appearance 
of the second pronephric funnel in the region of the limbs 
(Pl. X, Fig. 3). As the pronephric tubules increase in length 
they elongate at right angles to the direction of growth of the 
myotome-processes, and consequently push the myotome-proc- 
ess over against the somatopleuric thickening of the limb. The 
close proximity of the two structures seems to be due mainly 
to mechanical causes; 2z.¢., to the pressure exerted on the 
myotome-process by the elongating tubules. When the tubules 
become convoluted, later, they force their way in between the 
rudimentary limb and the myotomes, so that the connection 
between the myotomes and the ventral myotome-processes is 
broken (Pl. X, Figs. 6, 7). Maurer? has already shown these 
relations in the Urodela. 
1 Morph. Jahrb., Bd. 18, 1, 1891. Fig. 7, Pl. VI. 
