The central connexions of dorsal spinal nerve roots and the ascending tracts in the spinal cord of Lacerta viridis.

Until recently our knowledge of the detailed structure of the reptilian nervous system has been based almost entirely on observations made on serial sections of normal material prepared by routine neuro-histological methods. Most of these observations were reported in the older literature and were ably summarised by Kappers, Huber & Crosby, in 1936. In spite of the well-known limitations of the methods a considerable body of knowledge has been built up. Its interpretation, however, in terms of connexions between different parts of the nervous system, has depended in many cases on a presumed homology with tracts or collections of nerve cells similarly situated in the mammalian nervous system, where they have been subjected to more rigorous investigation by experimental methods. Recently, several papers have appeared in which the results of the differential staining of degenerating fibres or cells have been described in the reptilian brain. The degeneration has been caused by lesions so placed that it should demonstrate the connexions of particular nerves or parts of the brain, e.g. Armstrong (1950) for optic connexions, Gamble (1952) for olfactory connexions, and Powell & Kruger (1960) for striato-thalamic connexions. So far this work has been limited to the foreand mid-brain, where it has demonstrated many fundamental differences between reptilian and mammalian anatomy which could not have been demonstrated conclusively in preparations of normal material. The present investigation extends observations of this kind to lower levels of the nervous system and its main purpose is to determine the central connexions of the dorsal roots of spinal nerves and the course and destination of long ascending tracts in the spinal cord.