Anatomical and morphometric evaluation of the orbit, eye tunics, eyelids and orbital glands of the captive females of the South African painted dog (Lycaon pictus pictus Temminck, 1820) (Caniformia: Canidae)

Abstract

In this study, we present the first data concerning the anatomical, morphometrical, histological and histochemical study of the orbit, eye tunics, eyelids and orbital glands in South African Painted Dogs (Lycaon pictus pictus). The study was performed using eyeball morphometry, analysis of the bony orbit including its morphometry, macroscopic study, morphometry, histological examination of the eye tunics and chosen accessory organs of the eye and histochemical analysis. The orbit was funnel shaped and was open-type. There was a single ethmoid opening for the ethmoid nerve on the orbital lamina. The pupil was round, while the ciliary body occupied a relatively wide zone. The iris was brown and retina had a pigmented area. The cellular tapetum lucidum was semi-circular and milky and was composed of 14–17 layers of tapetal cells arranged in a bricklike structure. In the lower eyelid, there was a single conjunctival lymph nodule aggregate. One or two additional large conjunctval folds were observed within the posterior surface of the upper eyelids. The superficial gland of the third eyelid had a serous nature. The third eyelid was T-shaped and was composed of hyaline tissue. Two to three conjunctival lymph nodul aggregates were present within the bulbar conjunctiva of the third eyelid. The lacrimal gland produced a sero-mucous secretion. A detailed anatomic analysis of the eye area in the captive South African Painted Dogs females showed the similarities (especially in the histological examination of the eyetunics and orbital glands) as well as the differences between the Painted dog and the other representatives of Canidae. The differences included the shape and size od the orbita with comparison to the domestic dog. Such differences in the orbit measurements are most likely associated with the skull type, which are defined in relation to domestic dogs. The presented results significantly expand the existing knowledge on comparative anatomy in the orbit, eye and chosen accessory organs in wild Canidae.

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

“…The obtained results of the eyeball macroscopic measurements performed in the examined Asiatic black bear were similar to the brown bear, American black bear Ursus americanus , grizzly bear Ursus arctos horribilis and sloth bear Melursus ursinus [ 26 , 66 ], but also they were similar to the measurements made on some representatives of the Canidae family (crab-eating fox Cerdocyon thous , Arctic fox Alopex lagopus and bush dog Speothos venaticus ) compared to mongrel dogs, South African painted dog Lycaon pictus , wolves Canis lupus , gray fox Urocyon cinereoargenteus and red fox Vulpes , where the eyeball measurements were characterized by much higher parameters [ 25 , 66 , 67 , 68 ]. However, some species of Mustelidae and the only representative of Ailuridae red panda Ailurus fulgens [ 25 , 66 , 69 ] are characterized by small and medium dimensions of the eyeball compared to Ursidae and Canidae.…”

“…However, some species of Mustelidae and the only representative of Ailuridae red panda Ailurus fulgens [ 25 , 66 , 69 ] are characterized by small and medium dimensions of the eyeball compared to Ursidae and Canidae. The greatest differences in the dimensions of the eyeball within the Canidae family will be characteristic of domestic dogs, and in particular purebred dogs, and most likely it will be related to differences in craniometry, the type of skull (dolichocephalic, mesocephalic and brachycephalic) and the dimensions of the eye socket, which in the case of a domestic dog are correlated with the size of the animal [ 68 , 70 ]. According to Heard-Booth and Kirk, 2012 [ 66 ], the size of vertebrate eyes depends on body or head size, diet and activity pattern.…”

“…The maximum and minimum corneal diameter in the examined Asiatic black bear was similar to the other Ursidae species ( Ursus americanus , Ursus arctos , Melursus ursinus ) as well as in some wild Canidae species ( Alopex lagopus , Cerdocyon thous , Urocyon cinereoargenteus ) or in Procyonidae ( Bassariscus astutus , Procyon lotor ) [ 25 ]. Histological studies revealed that the cornea in the examined Asiatic black bear consists of only four layers because Bowman’s membrane was not found, as well as in domestic dogs, wolves, dingo Canis dingo and corsac fox Vulpes corsac [ 84 , 85 ], while it occurs in the South African painted dog [ 68 ]. In the Asiatic black bear, the anterior corneal epithelium consists of 5–6 layers of nucleated cells in the peripheral part and 6–7 layers of cells in the axial part, where a similar number of layers could be observed in Canis dingo , Canis familiaris , Cerdocyon thous and Vulpes corsac [ 86 ], while Canis lupus and Lycaon pictus were slightly higher [ 68 , 85 , 86 , 87 , 88 ].…”

“…Histological studies revealed that the cornea in the examined Asiatic black bear consists of only four layers because Bowman’s membrane was not found, as well as in domestic dogs, wolves, dingo Canis dingo and corsac fox Vulpes corsac [ 84 , 85 ], while it occurs in the South African painted dog [ 68 ]. In the Asiatic black bear, the anterior corneal epithelium consists of 5–6 layers of nucleated cells in the peripheral part and 6–7 layers of cells in the axial part, where a similar number of layers could be observed in Canis dingo , Canis familiaris , Cerdocyon thous and Vulpes corsac [ 86 ], while Canis lupus and Lycaon pictus were slightly higher [ 68 , 85 , 86 , 87 , 88 ]. Nautscher et al, 2016 [ 85 ], showed in their studies that the number of cell rows correlates with the corneal thickness, and that the thickness of the cornea changes with the age of the subject [ 85 ].…”

“…Nautscher et al, 2016 [ 85 ], showed in their studies that the number of cell rows correlates with the corneal thickness, and that the thickness of the cornea changes with the age of the subject [ 85 ]. The results of histometric measurements of the corneal layers in Asiatic black bear showed similarity to some wild Canidae ( Canis dingo and Vulpes corsac ), while higher values of these dimensions occurred in the domestic dogs and South African painted dogs [ 68 , 84 ]. In the pinnipeds, the cornea is characterized by a central flattened stripe in the vertical meridian and the near-spherical shape of the eyeball [ 84 , 89 , 90 ], as well as in the sea otter Enhydra lutra , where the eyeball is similar to those terrestrial mammals—it is almost spherical and the axial eye length is only a little shorter than the diameter, but the corneal curvature has very low convexity [ 83 ].…”