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The distinctive long neck of the giraffe (Giraffa camelopardalis) entails functional difficulties brought about by the extended distance between the heart and the head. Blood must be circulated over 2 m from the heart to the brain against gravitational force. The natural movement of the head to ground level would result in a large volume of blood moving toward the brain with the force of gravity. Large blood volumes also rush to the brain during bulls’ fighting (necking), rendering the giraffe susceptible to possible brain damage. The natural movement of the head from ground level to fully erect would result in blood moving away from the brain with gravitational force. The lack of blood perfusing the brain can cause fainting. The giraffe, however, suffers neither brain damage nor fainting. What adaptations do giraffes have to counteract these challenges? The aim of this study was to investigate the functionality of the rostral epidural rete mirabile situated just beneath the brain and its possible contribution to successful circulation in long-necked giraffes. The unique rostral epidural rete mirabile structure significantly contributes to counteract physiological challenges. Turns and bends characterize this structural arterial meshwork and subsequently an increased artery length through which blood flow must proceed before entrance into the brain, exerting resistance to blood racing to the brain when the head is lowered to the ground. The brain is supplied mainly by the maxillary artery through the carotid rete, with a rudimentary basilar artery not contributing to the brain’s blood supply. The resistance to blood flow due to the structure and position of the rostral epidural rete mirabile when the head is in the upright position is counteracted by the unique carotid-vertebral anastomosis allowing immediate cerebral blood supply. The rostral epidural rete mirabile structure in giraffes is an essential feature balancing physiological difficulties arising due to the extensive heart-to-head distance and might fulfill the same function in other long-necked artiodactyls.

The artiodactyl brain has multiple levels of vascular pooling and the rostral epidural rete mirabile (RERM) at its base. The current study is the first of its kind to precisely demonstrate the arterial vasculature of the dromedary brain, utilizing a new casting method with colored latex and epoxy paint. In total, 35 freshly slaughtered dromedary heads were injected with colored latex or colored epoxy paint prior to dissection in order to reveal cerebral vasculature; Ten processed heads were chemically digested with 5% potassium hydroxide to obtain hard casts of cerebral arteries and anastomosing structures. The outcomes of this study ascertain the distinct vascular features of dromedaries that set them apart from other artiodactyls. In addition to the RERM, the dromedary possesses a well-developed ophthalmic and chiasmatic rete. The dromedary is similar to giraffe, goat, cat and pig in the contribution of middle meningeal artery to the rete mirabile; however, dromedaries have several arteries emerging directly from the cerebral arterial circle that supply the choroid plexus and pineal gland. Additionally, dromedaries exhibit a dominant basilar system that dominates the blood supply to the medulla oblongata, pons, and cerebellum. In our study, we were able to graphically prove the lack of connection between the areas supplied by vertebrobasilar system and carotid system in the dromedary. Furthermore, the vertebral artery does not branch into the basilar artery; instead, it acts as a contributing vessel to the ventral spinal artery that later fuse to form the basilar artery. This study employed the new casting method to illustrate a new arterial source to RERM and the various anastomoses among arterial sources supplying the brain in the dromedary. These anastomoses play an important role in maintaining an uninterrupted cerebral blood supply, decreasing the vulnerability of the fragile brain against ischemia and stroke, as well as, play an important role in maintaining blood pressure and flow in long-necked dromedaries when they raise or lower their heads.

The artiodactyl brain has multiple levels of vascular pooling and the rostral epidural rete mirabile (RERM) at its base. The current study is the first of its kind to precisely demonstrate the arterial vasculature of the dromedary brain, utilizing a new casting method with colored latex and epoxy paint. In total, 35 freshly slaughtered dromedary heads were injected with colored latex or colored epoxy paint prior to dissection in order to reveal cerebral vasculature; Ten processed heads were chemically digested with 5% potassium hydroxide to obtain hard casts of cerebral arteries and anastomosing structures. The outcomes of this study ascertain the distinct vascular features of dromedaries that set them apart from other artiodactyls. In addition to the RERM, the dromedary possesses a well-developed ophthalmic and chiasmatic rete. The dromedary is similar to giraffe, goat, cat and pig in the contribution of middle meningeal artery to the rete mirabile; however, dromedaries have several arteries emerging directly from the cerebral arterial circle that supply the choroid plexus and pineal gland. Additionally, dromedaries exhibit a dominant basilar system that dominates the blood supply to the medulla oblongata, pons, and cerebellum. In our study, we were able to graphically prove the lack of connection between the areas supplied by vertebrobasilar system and carotid system in the dromedary. Furthermore, the vertebral artery does not branch into the basilar artery; instead, it acts as a contributing vessel to the ventral spinal artery that later fuse to form the basilar artery. This study employed the new casting method to illustrate a new arterial source to RERM and the various anastomoses among arterial sources supplying the brain in the dromedary. These anastomoses play an important role in maintaining an uninterrupted cerebral blood supply, decreasing the vulnerability of the fragile brain against ischemia and stroke, as well as, play an important role in maintaining blood pressure and flow in long-necked dromedaries when they raise or lower their heads.

Mammals with a carotid rete are capable of reducing brain temperature below that of carotid blood temperature, termed selective brain cooling. In artiodactyls, selective brain cooling conserves body water and may provide them with a selective advantage in conditions of increased temperature and aridity., Some mammals have the ability to lower their hypothalamic temperature below that of carotid arterial blood temperature, a process termed selective brain cooling. Although the requisite anatomical structure that facilitates this physiological process, the carotid rete, is present in members of the Cetartiodactyla, Felidae and Canidae, the carotid rete is particularly well developed in the artiodactyls, e.g. antelopes, cattle, sheep and goats. First described in the domestic cat, the seemingly obvious function initially attributed to selective brain cooling was that of protecting the brain from thermal damage. However, hyperthermia is not a prerequisite for selective brain cooling, and selective brain cooling can be exhibited at all times of the day, even when carotid arterial blood temperature is relatively low. More recently, it has been shown that selective brain cooling functions primarily as a water-conservation mechanism, allowing artiodactyls to save more than half of their daily water requirements. Here, we argue that the evolutionary success of the artiodactyls may, in part, be attributed to the evolution of the carotid rete and the resulting ability to conserve body water during past environmental conditions, and we suggest that this group of mammals may therefore have a selective advantage in the hotter and drier conditions associated with current anthropogenic climate change. A better understanding of how selective brain cooling provides physiological plasticity to mammals in changing environments will improve our ability to predict their responses and to implement appropriate conservation measures.

Atalgan, Şükrü Hakan (Balikesir Author), Rete mirabile epidurale rostrale küçük ruminantlarda cavum cranii içinde, hipofiz bezinin her iki yanında, sinus cavernosus içinde yer alan ve beynin arteriel kan akışını düzenleyen bir yapıdır. Bu çalışmada, Takilon ile korozyon kast tekniği kullanılarak, Bolu bölgesinden temin edilmiş 10 adet Saanen tekesinde (11 aylık, yaklaşık 42 kg ağırlığında ve şecereli) rete mirabile epidurale rostrale’nin yapısal özellikleri gözlemlenmiştir. Yapılan diseksiyonda bu anatomik yapının, genel özellikleri itibariyle diğer küçük ruminant türlerinde gözlemlenen yapı ile benzerlik gösterdiği belirlenmiştir. Bu atardamar ağının sadece arteria maxillaris’ten köken alan dallar tarafından oluşturulduğu ortaya konmuştur. Sağ ve sol tarafta yer alan ve üçgen görünümlü olan ağ bölümlerinin (pars dextra ve pars sinistra) ağızlaşarak ön tarafta ‘’V’’ şeklinde bir yapı oluşturduğu gözlemlenmiştir. Fakat bu ağızlaşma bir bireyde görülmemiştir. Ayrıca, atardamar ağının sağ ve sol yarımının makroskopik görünümleri arasında bir farklılık bulunmamıştır. Arteria maxillaris, ramus caudalis ad rete mirabile epidurale rostrale, rami rostrales ad rete mirabile epidurale rostrale adlı dallar korozyon kast tekniği ile net bir şekilde ortaya çıkartılmıştır. Yine, diseke edilen hayvanlarda rete mirabile epidurale caudale ve rete chiasmaticum’un şekillenmediği ortaya konulmuştur., The rostral epidural rete mirabile in small ruminants is bilaterally located next to the hypophysis in the cranial cavity, lies in the cavernous sinus, and regulates arterial blood flow of the brain. In this study, structural peculiarity of the rostral epidural rete mirabile in the ten male mature Saanen goats (11 months old, approximately 42 kg in weight, with a known pedigree, and obtained from Bolu region) was examined by corrosion cast technique using Takilon. Dissections have demonstrated that general architecture of the rostral epidural rete mirabile in the Saanen goat agrees with that in other small ruminants. It is structured by the branches from the arteria maxillaris only. The triangular shaped right and left components (the right and left parts) anastomose, forming a rostrally V-shaped structure. This anastomose was not observed in one of the materials. Thus, gross views and diameters of the retial arteries were not markedly different on the left and right sides. The maxillary artery, the rostral and caudal rami, and the rostral epidural rete mirabile were visualized by the corrosion cast technique. The caudal epidural rete mirabile and the chiasmatic rete were observed to lack in the Saanen goat.