LIMB FIELD OPERATIONS 



281 



vffji 



fig. 2 



obimetllartd ex. 



ANTERIOR LIMB AND GIRDLE OF AMBLYSTOMA PUNCTATUM 



Fig. 1. Medial view of the skeleton of the left anterior limb and girdle of Amblystoma punctatum, 



showing the areas of attachment of the muscles (length 44 mm. ). 

 Fig. 2. Lateral view of the skeleton of the left anterior limb and girdle of A. punctotum, showing the 



areas of attachnTent of the muscles (length 44 mm. ). 



ABBREVIATIONS USED IN FIGURES 1 AND 2 



C, centrale 



Ce, carpale 



Co, coracoid 



H, humerus 



I, intermedium 



Lat. Ep. , lateral epicondyle 



M, metacarpale 



Med. Ep. , medial Epicondyle 



PCo, procoracoid 



Ph, phalanges 



Proc. Lot., lateral process 



R, radius 



Re, radiale 



Sc, scapula 



SSc, suprascapula 



U, ulna 



Ue, ulnare 



DISCUSSION: 



From I. W. H. Blount 1935: Jour. Exp. Zool. 69:407 



The time at which the antero-posterior axis of the limb field has been irreversibly po- 

 larized has pushed back to the slit blastopore stage (Detwiler, 1933). The dor so-ventral 

 axis undergoes permanent polarization during stages #33 and #34. The relationship of 

 the ectoderm and the mesoderm in partial transplants suggests that the specific form of 

 the limb is probably contained within the mesodermal portion of the limb-field while the 

 ectodermal covering maintains a passive relation to the growth pattern of the underlying 

 mesoderm. The fusion of transplants, splitting and twinning of limbs, altering of axes, 

 and the relation of the girdles all indicate that the fundamental limb forming material is 

 primarily mesodermal. 



