Both cats and dogs belong to animals with the same type of limb support but have different nature of movement. Despite belonging to digitigrade animals, cats and dogs have a different nature of motion. While moving, the medial joint surface in cats and lateral surface in dogs carry the larger pressure. The aim of the study was to compare the similar surfaces of the cat's and dog's tarsal joint capsule and to detect differences in its histostructure and vascularisation. For the study, we used the capsule of the tarsal joint of five cats and five dogs dissected with accordance to anatomical surfaces. Sections of the capsule joint were stained with haematoxylineosin. The sections were examined with a microscope at magnification ×250 and ×400. The statistical analysis of the results was done using Student's t test. During the research, a difference in histostructure and vascularisation of tarsal joint capsule in cats and dogs on respective surfaces were found. The medial surface of the tarsal joint capsule was the most saturated with hemomicrocirculatory bed structures in cats, whereas this was the lateral surface in dogs. The most active metabolic processes also take place in these areas of the joint capsule, which is important to know when prescribing therapeutic procedures and determining an optimal surgical access.

The comparative studies of the tarsal joint capsule of cattle (Bos taurus) and canines (Canis lupus) have clarified general patterns of the structural organization of a joint capsule and the species-specific features of its angioarchitectonics. The differences in the formation of the fibroelastic layer and the location of vascular fields in the cases of animals with different stances were established. The zones of intensive intraorganic vascularization of the joint capsule were revealed; that being—the plantar and dorsal surface in the case of cattle, the lateral and medial surfaces—in case of the canine.

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Meniscus injuries are recognized as the cause of significant morbidity of the musculoskeletal system. Features of the structural organization of the various meniscus zones are a necessaryfor understanding pathologies associated with the knee joint. This will expand and deepen micromorphological knowledge and practically apply during the choice of treatment tactics for meniscus preservation, suturing during reconstructive meniscus repair, reduce the risk of vascular injuries, and make it possible to use tissue engineering for meniscus regeneration. Indeed, today it is known that only the preservation of menisci or a slight ectomy of the inner zone, which cannot be restored with signifi cant injury, can preserve the health and biomechanics of the knee joint. The aim of our work was to determine the characteristics of the cyto- and fi bromorphological characteristics, as well as the degree of vascularization of the external (red) zone of the lateral and medial menisci of the knee joint in foot-moving coypus. A complex of histological and neurohistological research methods was used in the work. The patented neurohistological method of impregnation is performed in its own algorithm. The selection of animals was carried out according to the type of specialization of the limb to the substrate. As a result of histological examination, it was found that cyto-fi broarchitectonics of the external (red) zone of the latera l and medial menisci of the coypus has general biological signs, and species-specifi city is characteristic of vascularization. The external (red) zone of the coypu’s meniscus is similar in st ructure to the dense, formed connective tissue. Cytoarchitectonics is represented by of the fi broblastic typecells: fi brocytes, fi broblasts and undiff erentiated stem cells, which are localized between collagen fi bers individually, in pairs, in a chain or in short rows. Fibroarchitectonics – tightly packed bundles of collagen fi bers with a pronounced parallel orientation. The medial meniscus has saturated zones of intraorgan vascular nutrition due to dilated, anastomosing capillary branches formed by perforations with perimeniscal broad-loop microcirculation nets that occupy large areas and form vascular fi elds, as well as numerous vascular glomeruli. In the lateral meniscus, the vascularization zone is characterized by limited capillary branches, interval and small penetration by capillaries of the meniscus red zone, and limited, localized perimeniscal nets. Key words: fi brocytes, fi broblasts, collagen fi bers, vascularization, vascular glomeruli, external zone, red zone, meniscus, knee joint, coypu.

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.