Cerny H., L. Brandstatter: The Development of Rudimentary Metapodial and Acropodial Skeletons in the Sheep. Acta vet. Bmo, 1990: 3-11. On the material obtained from six embryos (CRL 18-35 mm), 48 foetuses CRL 70-280 mm) and 12 sheep (14 days-15 months) we investigated the development of the rudimentary skeleton of the metapodium and acropodium in tissue sections using light microscopy. The sections were stained with hematoxylin and eosin, according to van Gieson, with alcian blue and a mixture of Ponceau 2K and acid fuchsin. Mineralization du ring ossification was ascertained by a histochemical calcium examination according to Kossa. The material from the postnatal period was processed by osteological and radiographical methods. The change of the mesenchymal skeleton of the second an fifth primordia of the metapodium into cartilaginous skeleton in the sheep occurs in its late embryonal stage. In this period, the metapodial skeleton becomes clearly differentiated into the main and the rudimentary skeletons, the cartilaginous skeleton of the lateral primordium becoming markedly reduced in comparison with the axial ones. The mesenchymal skeleton of lateral primordia is not subject to a change into embryonal cartilage in its full extent. It morphologically differentiates into the pro ximal skeleton of the second and fifth metapodials and the distal skeleton of the acro podial. The two skeletons are connected by an original mesenchymal blastema. In the course of the development, the metapodial skeleton ossifies, the development of rudimentary skeletons of the second and fifth digits ceases when it reaches the cartilaginous tage. Ossification of the second and fifth metapodials begins on the 50th day of prenatal development in the foetus of CRL 90 mm, i. e. about 7 days later than ossification of the main skeleton, and corresponds to the diaphyseal ossification of the long bone. Calcium distribution showed predominance of the resorption phase over the osteo genous phase during ossification. As a result, distal segments of the skeleton are completely resorbed and only their proximal segments are preserved in the postnatal period. The rudiment of the fifth metacarpal is a needle-shaped bone with a head, whose length varies greatly from case to case. It forms a syndesmotic connection with the fourth metacarpal. The second metacarpal is often missing or appears only as a tiny rudiment synostotically connected to the base of the third metacarpal. Ru diments of the second and fifth metacarpals cannot be demonstrated in the definitive skeleton, because they have been fully resorbed. The one- or two-phalanx skeleton of the acropodium is a cartilaginous cylinder. Proximally, it extends as far as the base of proximal sesamoid bones, while distally it reaches connective structures of the differentiating subcutis. It never ossifies, its development being terminated in the stage of cartilaginous skeleton, which is com pletely replaced by connective tissue already during the prenatal development.