Relations of the shoulder girdle to the embryonic and adult anatomy.

<p>According to the fate map by Stocum and Fallon <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0052244#pone.0052244-Stocum1" target="_blank">[32]</a>, the shoulder girdle of the axolotl arises mainly from flank mesoderm as part of the embryonic limb field (left). The upper, scapular (sca), and the lower, coracoid (cor) parts of the shoulder girdle (right) originate from the specific areas of the limb field around the region, which gives rise to cartilage and connective tissues of the prospective free limb (fl) <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0052244#pone.0052244-Stocum1" target="_blank">[32]</a>. The shoulder girdle region is thus positioned just caudal to the branchial arches (ba), where the main streems of migrating neural crest cells pass. In adults, the coracoid plate of one side meets the contralateral counterpart along the ventral midline of the animal, while the upper scapular edge reaches the level of transverse processes of the thoracic vertebrae. These parts of the shoulder girdle are cartilaginous (grey) in the axolotl throughout life, while the middle of the shoulder girdle (both in the scapula and the coracoid plate), from where the limb emerges, are ossified in adults. The anterior, cranial edge of the scapula bears the attachment sites of muscles (m. cuccularis, m. opercularis), which connect the shoulder girdle to the occipital bones of the skull. Other abbreviations: e, eye; prn, pronephros; s, somite, tv, thoracic vertebrae. Not to scale.