Anatomy of Normal and Reduplicated Limbs in Urodeles

Abstract

A study of the anatomy of double limbs in urodeles with especial reference to musculature and blood vessels was made as a basis for a further understanding of the process of reduplication.

Double limbs were produced by rotation of the fore limb bud, both in the normal position and 3-5 segments posterior, in a number of species of Amblystoma (Ambystoma) and in Eurycea bislineata. Statistical treatment revealed specific differences in the proportions of total suppression, of reduplication and the subsequent resorption of one member of the pair. More cases of reduplication occurred in those species in which the growth of the limbs is most rapid. Most frequent resorption of one member, however, was found in those with the fastest general growth. A. tigrinum showed the greatest number of cases of total suppression. Limbs transplanted to the flank were more often completely suppressed than were the ones rotated in the orthotopic position, but among the reduplications fewer members were resorbed.

The musculature of double limbs was found to be reduplicated from a point slightly proximal to the junction of the members. While distally the muscles of double limbs in the orthotopic position were entirely similar to those of the heterotopic limbs, the shoulder muscles of these series differed in 2 ways. First, the intrinsic muscles were found in the heterotopic limbs only if the parts of the girdle to which they are normally attached were present, and since only 31/2-somite grafts were taken, the heterotopic girdles were often mere plates representing just the central portion of the girdle. Second, the 4 extrinsic muscles which are derived from the myotomes and the gill musculature were never found in the heterotopic limbs, although the latissimus dorsi and the pectoralis, which develop from the limb itself, were usually present.