Limb Girdles

LIMB GIRDLES, skeletal formations that serve as support for the free limbs of vertebrates. Corresponding to the two pairs of limbs, there is a distinction between the anterior pectoral girdle (see) and the posterior pelvic girdle (see Pelvic girdle). In their development, these formations are most closely connected with the skeleton of the limb itself. The early rudiment of the girdle is formed together with the rudiment of the free limb from a collection of skeletogenic mesenchyme, which arises by proliferation from the parietal layer of the lateral plate and concentrates at the base of the limb rudiment. Initially quite homogeneous, the blastema then grows on one side, in the distal direction, into the limb rudiment, where it differentiates, forming the rudiments of individual rays, and on the other side into the wall of the body itself, partly in the dorsal and especially in the ventral direction. The part of the blastema that grows into the wall of the body itself represents the rudiment of the limb girdle. The separation of the latter from the skeleton of the free limb is the result of ossification, which occurs in the girdle independently of the elements of the limb itself (see Pectoral girdle).