H 0 r k yD., F. Tic h y: Ultrastructure of Feline Articular Cartilage in the Postnatal Period. Acta vet. Brno, 1995, 64: 63-70.Articular cartilage was investigated in five cats of both sexes, aged 1,21 and 43 days, and in two adult cats aged 5 years. Samples for transmission electron microscopy were collected from femoral heads and processed using conventional techniques. The object of the investigations was cellular structures and intercellular matrix of the superficial, middle and deep layers, but not those of transition cells and the tide-mark region.In the superficial layer of the samples collected from 1-, 21-and 43-day old kittens, chondrocytes were found mostly in pairs sharing a common lacuna surrounded with well formed pericellular matrix.Reticular-type nucleoli were usually present in nuclei, and scarce small mitochondria, dilated GER (granular endoplasmic reticulum) cisternae and transport vacuoles were observed in cytoplasm. Towards the middle layer, cell membranes of chondrocytes contacted the intercellular matrix. The surface of the articular cartilage was covered by a continuous and well formed chondrosynovial membrane. Areas with various appearances can be distinguished in the cartilages of adult cats. Continuous chondrosynovial membrane covered a thick layer of intercellular matrix with scarce chondrocytes in undamaged areas, while other areas showed signs of various degrees of damage.No differences in the structure of the middle layer were found among the various age groups. Oval or spherical chondrocytes contain large nuclei and cytoplasm contains numerous GER cisternae, mitochondria, Golgi's complex, numerous smooth vesicles, sporadic lysosomes and rare centrioles and lipid droplets. Pericellular matrix had almost disappeared and cell membrane contacted closely the intercellular matrix.The deep layer of the articular cartilage of 1-, 21-and 43-day-old kittens contained lacunae harbouring either single chondrocytes or pairs thereof arranged perpendicularly to the surface. The spindle-shaped cells were smaller and contained a lesser amount of organelles than their counterparts in the middle and the surface layers. The pattern of the intercellular matrix was similar to that of the middle layer. In addition to intact chondrocytes with a normal structure of cytoplasm and nucleus, the deep layer of the adult cartilage contained degenerated cells with large lipid droplets, glycogen deposits, disintegrated mitochondria and pyknotic nuclei.