Morphology and Histology of the Orbital Region and Eye of the Asiatic Black Bear (Ursus thibetanus)—Similarities and Differences within the Caniformia Suborder

Abstract

In this study, we present first data concerning the morphological observations of the orbital region, eye tunics, upper and lower eyelids, superficial gland of the third eyelid with the third eyelid, and lacrimal gland in captive adult male Asiatic black bear. The following research methods were used in the work: the eyeball morphometry, the orbital region description, macroscopic description, morphometric and histological analysis of the eye tunics and selected the accessory organs of the eye (Fontana–Masson, hematoxylin & eosin (H&E), Methyl-green-pyronin Y (MGP Y), Movat pentachrome, and picro-Mallory trichrome) as well as histochemical examination (PAS, AB pH 1.0, AB pH 2.5, AB pH 2.5/PAS and HDI). The eyeball of the Asiatic black bear was a spherical shape, while the periorbita was funnel/conical-shaped and the eye socket was of the open type. The cornea was absent of the Bowman’s membrane similar to all domestic dogs and some wild dogs. There were palisades of Vogt in the corneal limbus epithelium similar to the Canidae. Degenerative choroidal tapetum lucidum similar to ranch mink (Mustelidae) has been found. The pupil was big and round in shape. The ciliary muscle, dilatator and sphincter muscle were well developed, similar to the pinnipeds. The lens was biconvex round, similar to the Canidae. The retina was composed similarly to the diurnal terrestrial carnivores. In both eyelids were observed very well-developed tarsal glands, ciliary glands and sebaceous glands. The orbital zone in the eyelids was characterized by lymphoid follicles, diffuse lymphocytes and specialized high endothelial venules. In the anterior palpebral margin of the upper eyelid, soft and short eyelashes were observed, while in the lower eyelids they were absent. The third eyelid was T-shaped and composed of the hyaline tissue, and it contained CALT, similar to that in Canidae. The superficial gland of the third eyelid was a multilobar alveolar branched complex with seromucous nature, while the lacrimal gland was also a multilobar acinar branched complex gland, but producing a mucous–serous secretion. The results of our research indicate that the features of the anatomy of the eye and orbital region in Asiatic black bear are also typical of the Ursidae family. Moreover, a detailed analysis of the morphological eye region may be useful in comparative studies and veterinary diagnostics in this bear species.

The organ of vision morphology of the southern two‐toed sloth (Choloepus didactylus Linnaeus, 1758; Pilosa, Choloepodidae)

“…Macroscopically, the tapetum lucidum in the southern two‐toed sloth was not identified, as was the case with Bradypus variegatus (Braz et al, 2020; Sena et al, 2021), while our histological studies showed the presence of choroidal tapetum lucidum cellulosum , the cells of this latter being characterized by folding of the cell membrane and irregular layering. Such structure of tapetum lucidum proves its degeneration, which was similarly demonstrated in the Asiatic black bear ( Ursus thibetanus ; Paszta et al, 2022) and ranch mink ( Mustela vision ; Braekevelt, 1989; Ollivier et al, 2004). Ollivier et al (2004) report that the cause of this wallpaper degeneration is unknown but could be related to dietary insufficiencies in specific animals, or perhaps the genetics of inbreeding.…”

Morphological examination of the visual system and orbital region in the red panda (Ailurus fulgens fulgens)

“…A detailed anatomical description of the orbital region in the examined red panda reveals that its orbits are of an open type, similar to those of Canidae, Ursidae, and the Musteloidea clade. This orbit is composed of similar bony structures, although differences among the aforementioned groups were also observed [ 46 , 60 – 66 ]. Common features shared by Canidae, Ursidae, and the Musteloidea clade include the absence of a supraorbital foramen and the presence of an infraorbital foramen [ 62 – 66 ].…”

“…Significant differences exist not only between Canidae and Ursidae but also within these families and the Musteloidea clade itself. Features common to Ailuridae, Canidae, and Ursidae include the presence of an optic canal, orbital fissure, foramen rotundum, and rostral and caudal alar foramen with an alar canal [ 46 , 60 – 62 , 67 , 68 ]. The differences observed between Canidae, Ursidae, and Ailuridae include a single ethmoid foramen in the red panda, Asiatic black bear, and South African painted dog, whereas domestic dog has a double ethmoid foramen.…”

“…The differences observed between Canidae, Ursidae, and Ailuridae include a single ethmoid foramen in the red panda, Asiatic black bear, and South African painted dog, whereas domestic dog has a double ethmoid foramen. Additionally, fossa for the lacrimal sac is present in red pandas studied by us, as well as in Asiatic black bear, and domestic dog but absent in South African painted dog [ 46 , 60 – 62 , 66 ]. A shared feature among Ailuridae, Canidae, and Musteloidea clade is the presence of a narrow, short, and pointed zygomatic process of the frontal bone.…”

“…Due to the absence of females and the limited number of subjects in this study, we cannot definitively determine the influence of sexual dimorphism on these dimensions. Macroscopic studies of both eyelids in two male red pandas revealed the presence of eyelashes exclusively on the UE, a pattern shared with domestic dog, wild dogs (such as the South African painted dog and crab-eating fox), ring-tailed coati, and the Asiatic black bear [ 60 – 62 , 70 , 71 ]. Carvalho et al [ 70 , 72 ] noted that both the maned wolf and the crab-eating fox exhibit short and sparse accessory eyelashes on the LE, whereas ring-tailed coatis possess a hairy caruncle.…”