The study of segmental innervation may be of practical interest, as pathological processes involving organs and tissues can be caused by damage to both peripheral and individual segmental nerves. Also, the occurrence of a pathological condition of the pelvic limb structures can be associated with various injuries, damage to the spinal cord, roots and segmental nerves of the sacral spine. The aim of the experimental research was to study the segmental formation of the main nerves of the sacral plexus – n. ischiadicus, n. tibialis, n. peroneus communis in cats. Unilateral extravertebral ganglioectomy of the lumbosacral segments – L 4, L5, L6, L7, S1, S2 was performed for the study. Samples of the main nerves were examined in polarized light to detect signs of Wallerian's degeneration at x400 magnification. This method allows you to easily distinguish degenerated nerve fibers at different stages of degeneration from normal. The micromorphology of the initial stages of degeneration is characterized by uneven thickening of the fibers, smoothing of the Ranvier nodes, dilated Schmidt-Lanterman notches, an increasein the number of myelin segments. At later stages of Wallerian's degeneration, the following are observed: edema and significant thickening of the myelin sheath, smoothing of fiber contours, formation of ovoids and fragmentary glow of myelin. Statistical analysis of the results was performed using Student's t-test. In the course of research, it was found that in the formation of the main nerves of the sacral plexus: n. ischiadicus, n. tibialis, n. peroneus communis involves 6 segments of the lumbosacral spine - from L4 to S2. These nerves of the sacral plexus are polysegmental, which indicates their compensatory properties. The highest percentage of degenerated nerve fibers for the main nerves of the sacral plexus gives the 6th lumbar segment L6, which is the axial nerve. The obtained results can expand the knowledge of principles of segmentation in anatomy, to become a reference point for sacral regional epidural anesthesia for orthopedic operations on the pelvic limbs, nerve blockade to increase patient comfort in the postoperative period, lumbar puncture, neurotherapy. The method of polarization microscopy can be used as a clinically useful test for peripheral nerve biopsy to assess the state of neurodegenerative changes, monitoring regenerative and neuroprotective effects.

Key words: Wallerian degeneration, segmental innervation, sacral plexus, polarization microscopy, cats.