SPINAL-CORD CENTRAL CANAL OF THE GERMAN-SHEPHERD DOG - MORPHOLOGICAL,HISTOLOGICAL, AND ULTRASTRUCTURAL CONSIDERATIONS

This study deals with some macroscopical, microscopical, and ultrastru ctural aspects of the spinal cord central canal of the German shepherd dog. The caudal end of the spinal cord is constituted by the conus me dullaris, which may extend to the first sacral vertebra, the terminal ventricle, and the filum terminale. The latter structure is considered as internum (second to third sacral vertebrae) or externum (fifth cau dal vertebra), according to its relation to the dura mater. Occasional ly, there is a second anchorage which is close to the level of the six th caudal vertebra. The central canal is surrounded by a ciliated epen dymal epithelium, which differs depending upon the levels. The most ca udal part of the filum terminale bears a columnar ciliated ependymal e pithelium surrounded by two layers of glia and pia mater, which separa te the central canal from the subarachnoid space. Microfil injections show a communication between the cavity and the subarachnoid space, as the plastic is able to pass through the ependymal epithelium. At the level of the terminal ventricle there are real separations of the epen dymal epithelium, which seem to connect the lumen of the spinal canal with the subarachnoid space. These structures probably constitute one of the drainage pathways of the cerebrospinal fluid. The diameter of t he central canal is related to the age of the animal. However, even in very old animals the spinal cord central canal reaches the tip of the filum terminale and remains patent until death. At the ultrastructura l level the ependymal cells present villi, located on cytoplasmic proj ections, cilia, dense mitochondria, and oval nuclei. (C) 1995 Wiley-Li ss, Inc.