116 BYRNES. [Vou. XIV. 
the coelomic cavity as aggregations of a few of the mesenchyme- 
like cells of the somatopleure. In the region of this meso- 
dermal thickening the ectoderm also becomes conspicuously 
thickened. Kaestner has already pointed out these relations 
in the development of the posterior limbs of Rana. 
After leaving its posterior attachment to the eleventh myo- 
tome, the abdominal muscle-rudiment (the ventral myotome- 
processes) skirts the anterior limit of the posterior limb, and 
as it passes forward and ventrally presses so close to the limb 
that it is often difficult to detect any boundary between the 
cells of the two structures (Pl. X, Fig. 12). Cross-sections 
through the posterior limb-region of Rana show the abdominal 
muscle elongated in the direction of the limb and having at 
times the appearance of a muscle-bud with a well-defined ven- 
tral boundary. Longitudinal sections, however (Pl. X, Fig. 12), 
show that this appearance is due only to the sectioning of an 
oblique structure, and that there are in reality no bud-like 
structures present. Directly in front of the limb-rudiment the 
abdominal muscle emerges at a level below the limb. 
The youngest larvae figured by Kaestner! are much too far 
advanced to show the closest connection between the posterior 
abdominal muscle-rudiment and the earliest rudiment of the 
posterior limbs. Pl. X, Figs. 12 and 18, show the normal rela- 
tions between the myotome, the posterior abdominal muscle, 
and the limb in a very young frog embryo in which the limbs 
are just beginning to develop. The only possible connection 
between the myotomes and the limb-rudiments in Rana is an 
indirect one through the abdominal muscle, which at a very 
early period comes into close contact with the limbs. But 
even here the connection between the limbs and the abdominal 
muscle is only apparent, as I hope to show in the chapter on 
experiments on Rana. 
Kaestner has been unable to demonstrate an ingrowth of 
any myotome-derivative into the limb-rudiment in Rana. He 
says : “So scheinen unsere Untersuchungen zu einem Resultat 
gefiihrt zu haben, welches im Widerspruch steht mit denen, 
die bisher an allen iibrigen Wirbelthier-Klassen gewonnen 
1 Archiv f. Anat. u. Phys., Hefte 5 und 6, 1893. 
