Bone metastasis may be the first sign that you have cancer, or bone metastasis may occur years after cancer treatment. Bone metastasis can cause pain and broken bones. With rare exceptions, cancer that has spread to the bones can't be cured. Treatments can help reduce pain and other symptoms of bone metastases.
Medical Definition of Chondrichthyes. : a class comprising cartilaginous fishes with well-developed jaws and including the sharks, skates, rays, chimeras, and extinct related formsâcompare cyclostomata.
Bony fishes can swim forward and backward.   Gills:   Both cartilaginous and bony fish have gill slits but the bony fish also have gill covers (an operculum).   Reproduction:   In the Chondrichthyes the males have claspers which assist in copulation. Fertilisation is internal-almost unique among fish. Scales:   Cartilaginous fish have large scales called placoid scales. These have a bone like base embedded in the skin and a backward projecting enamel covered dentine spine. The whole thing has a central pulp cavity (rather like the structure of teeth). The epidermis and dermis form placoid scales.