Background: Gerbils (Meriones unguiculatus) are rodents belonging to the Muridae family. Recently, breeding of this species as pets has increased significantly. Animal models are being investigated to study diseases related to the human aortic arch. Despite the importance of the aortic arch in maintaining homeostasis, there is limited data available regarding its morphology in gerbils. This study was performed with the objective of describing the collateral branches of the aortic arch in this animal to establish a standard model and thus contribute to future research on cardiovascular diseases in humans.Materials, Methods & Results: This study used 20 male specimens from previous studies that were frozen and stored at the Laboratory of Veterinary Anatomy of the Federal Rural University of the Semi-Arid Region. After thawing the animals, the thoracic cavity was opened for aortic cannulation. The vascular system was washed using saline solution and Neoprene latex stained with red pigment was injected. Subsequently, the animals were fixed in 10% formaldehyde and were dissected and analyzed 72 h later. The arrangement of the collateral branches of the aortic arch in gerbils was analyzed in all animals. The brachiocephalic trunk, the left common carotid, and the left subclavian artery were observed to originate as collateral branches. The brachiocephalic trunk bifurcated into the right common carotid and the right subclavian arteries. The right and the left subclavian arteries branched into the vertebral artery, the internal thoracic artery, the superficial cervical artery, the costocervical trunk, and the axillary artery.Discussion: Several studies reported in the literature describe the collateral branches of the aortic arch in domestic and wild mammalian species. These studies examined the main arteries that originate directly from the aortic arch and their respective branches, and classified the different anatomical variants of the aortic arch in each species. Three different arrangements have been commonly described. The first type corresponds only to the brachiocephalic artery originating from the aortic arch. The right and the left common carotid arteries and the right and the left subclavian arteries originate from this brachiocephalic artery. This type has already been described in the laboratory rat, catingueiro-deer, cattle, and horses. The second type is characterized by the presence of 2 arteries - the brachiocephalic trunk and the left subclavian artery. The right and the left common carotid arteries and the right subclavian artery originate from the brachiocephalic trunk. This arrangement has been reported in most species already studied such as rodents including the paca, chinchilla, guinea pig, mocó, nutria and the preá. The third type of vascular arrangement is observed in the gerbil. In this species, 3 collateral arteries originate from the aortic arch (the brachiocephalic trunk, the left common carotid, and the left subclavian artery). The right common carotid and the right subclavian artery originate from the brachiocephalic trunk. This vascular model has been described in the manatee, in humans, mice, sauim, and the monkey-nail. Thus, we concluded that the branching pattern of the aortic arch of the gerbil was characterized by the brachiocephalic trunk, the left common carotid, and the left subclavian artery, as has been described in mice, the manatee, monkey-nail, sauim, and humans. Based on these morphological characteristics, gerbils could serve as potential experimental models to study diseases related to the human aortic arch.

Background: The Rhea americana americana is a wild bird belonging to the group of Ratites, and is important from the scientific point of view given their adaptability to captivity. Considering that information about its morphology is important for the viability of domesticating the species, the aim of this study was to macroscopically identify the brain regions, as well as the cerebral arteries and the cerebral arterial circuit in order to establish the cerebral vascular pattern and systematization.Materials, Methods & Results: Twenty one brains from young and adult Greater Rheas of both sexes were used from animals that had died due to natural causes and were then kept in a freezer. The specimens were thawed and incised in the cervical region to allow exposure of the left common carotid artery, which was cannulated. The vascular system was rinsed with 0.9% saline solution, then perfused with latex Neoprene 650 stained with red pigment. The animals were subsequently fixed in 3.7% aqueous formaldehyde solution for 72 h, and then they were dissected by removing the bones from the skull cap. The brains were analyzed, and the structures were identified, photographed, schematized and denominated. Morphometric measurements were performed on the basilar and cerebellar ventral caudal arteries, recording the values of length and width in millimeters with the aid of a digital caliper. The brain was divided into: telencephalon, diencephalon, brainstem and cerebellum; while externally, the observed structures are: olfactory bulbs, optical lobes, optic nerves, optic chiasm, pituitary and pineal glands. Vascularization was performed by the following arteries: ventral spinal artery, basilar artery, ventricular cerebellar arteries, medium ventricular cerebellar arteries, caudal branches of the carotid arteries of the brain, ventral mesencephalic artery, cerebral caudal arteries, rostral branches of the carotid arteries of the brain, middle cerebral arteries, cerebroethmoidal arteries, rostral intercerebral anastomosis, rostral cerebral arteries, ethmoidal arteries, internal ophthalmic arteries, inter-hemispheric artery, pituitary arteries, dorsal mesencephalic tectal arteries, dorsal cerebellar arteries, occipital, pineal and dorsal hemispherical branches. The cerebral arterial circuit was both caudally and rostrally closed in 100.0% of the samples, being composed of the arteries: basilar artery, caudal branches of the carotid brain, rostral branches of the brain carotid, cerebroethmoidal arteries and rostral intercerebral anastomosis.Discussion: Encephalon classification regarding the presence or absence of gyri is a characteristic associated to evolutionary aspects among vertebrates, being respectively considered as lisencephalon or girencecephalus when it presents or does not present convolutions. In Greater Rheas, the telencephalon was quite developed, with a relatively rounded shape and the absence of sulci and convolutions in the cortex, which allowed it to be classified as a lisencephalon. Such findings resemble those described for the ostrich and in a comparative study involving kiwis, emus, owls and pigeons, although different sizes and forms of telencephalon development were observed in the latter. Regarding the cerebral arterial circuit, this structure in Rheas was complete and both caudally and rostrally closed in 100.0% of the specimens. Our findings differ from those observed for ostriches, in which a rostrally open behavior has been described, while it is caudally closed in 20.0% of cases and opened in 80.0%. Regarding the vascular type of the brain, in the Rhea it was observed that there was only contribution of the carotid system, similar to that found for birds such as ostriches and turkeys which confer a type I encephalic vascularization.