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The brain is particularly susceptible to increased blood temperature and to protect the brain from any potential heat stress a number of species have developed protective mechanisms with the ability to selectively cool the brain. This protective system is often referred to as the Rete Mirable. The Rete Mirable is a complex network of arteries and veins lying very close to each other and depends on a countercurrent blood flow between the arterioles and venules (blood flowing in opposite directions). It exchanges heat, ions, or gases between vessel walls so that the two bloodstreams within the rete maintain a gradient.  

The brain is particularly susceptible to increased blood temperature and to protect the brain from any potential heat stress a number of species have developed protective mechanisms with the ability to selectively cool the brain. This protective system is often referred to as the Rete Mirable. The Rete Mirable is a complex network of arteries and veins lying very close to each other and depends on a countercurrent blood flow between the arterioles and venules (blood flowing in opposite directions). It exchanges heat, ions, or gases between vessel walls so that the two bloodstreams within the rete maintain a gradient.  

==Venous Sinuses==

==Venous Sinuses==

Venous sinuses drain the brain, meninges, and surrounding bone as well as participate in cerebrospinal fluid resorption; they are arranged into two systems. The dorsal system is within the dura

Venous sinuses drain the [[Equine Brain - Horse Anatomy|brain]], [[Equine Meninges - Horse Anatomy|meninges]], and surrounding bone as well as participate in [[Equine Cerebrospinal Fluid - Horse Anatomy|cerebrospinal fluid]] resorption; they are arranged into two systems. The dorsal system is within the [[Equine Meninges - Horse Anatomy#Dura Mater|dura mater]] of the cranium and drains the [[Equine Brain - Horse Anatomy#Forebrain|cerebral cortex]], the cortex of the [[Equine Brain - Horse Anatomy#Hindbrain|cerebellum]], the deeper telencephalon, part of the diencephalon, and the tectum of the [[Equine Brain - Horse Anatomy#Midbrain|midbrain]].  The ventral (basilar) system lies on the floor of the cranial vault and drains the [[Equine Brain - Horse Anatomy#Hindbrain|brainstem]]. The dorsal and ventral systems have minimal connection between them, but each communicates with the extracranial venous system.  The dorsal system begins where several dorsal cerebral veins converge in the area of the '''crista galli''' of the '''cribriform plate'''.  

mater of the cranium and drains the cerebral cortex, the cortex of the cerebellum, the deeper telencephalon, part of the diencephalon, and the tectum of the midbrain.  The ventral (basilar) system lies on the floor of the cranial vault and drains the brainstem. The dorsal and ventral systems have minimal connection between them, but each communicates with the extracranial venous system.  The dorsal system begins where several dorsal cerebral veins converge in the area of the '''crista galli''' of the '''cribriform plate'''.  

The '''dorsal sagittal sinus''' arises from this convergence and runs caudally along the dorsal midline; surrounded by the falx cerebri as it lies against the skill bones.  Along its course, it receives '''cerebral veins''', '''meningeal veins''', and '''diploic veins''' from the skull.

The '''dorsal sagittal sinus''' arises from this convergence and runs caudally along the dorsal midline; surrounded by the falx cerebri as it lies against the skill bones.  Along its course, it receives '''cerebral veins''', '''meningeal veins''', and '''diploic veins''' from the skull. The dorsal sagittal sinus of the horse, is incompletely divided by a septum and bifurcates rostral to the '''osseous tentorium'''. Just before reaching the osseous tentorium, the dorsal sagittal sinus receives a single sinus that drains the '''medial cortex''', '''corpus callosum, '''basal ganglia''', and part of the '''diencephalon'''. The '''transverse sinuses''' run ventrally from the '''osseous tentorium''' to the '''retroarticular foramen''', where they exit to join the '''extracranial venous system'''. The transverse sinuses receive the '''dorsal petrosal sinuses''', which mainly drain the '''rhinencephalon'''. They also receive veins from the caudal [[Equine Brain - Horse Anatomy#Forebrain|cerebrum]], dorsal [[Equine Brain - Horse Anatomy#Midbrain|midbrain]] and the [[Equine Meninges - Horse Anatomy|meninges]]. The transverse sinuses are connected  via the '''communicating sinus''' without directly joining to the dorsal saggital sinus in the horse.

The dorsal sagittal sinus of the horse, is incompletely divided by a septum and bifurcates rostral to the '''osseous tentorium'''. Just before reaching the osseous tentorium, the dorsal sagittal sinus

receives a single sinus that drains the '''medial cortex''', '''corpus callosum, '''basal ganglia''', and part of the '''diencephalon'''. The '''transverse sinuses''' run ventrally from the '''osseous tentorium''' to the '''retroarticular foramen''', where they exit to join the '''extracranial venous system'''. The transverse sinuses receive the '''dorsal petrosal sinuses''', which mainly drain the '''rhinencephalon'''. They also receive veins from the caudal cerebrum, dorsal midbrain and the meninges. The transverse sinuses are connected  via the '''communicating sinus''' without directly joining to the dorsal saggital sinus in the horse.

The '''ventral sinus system''' contains the '''cavernous sinuses''', '''basilar sinus''', and '''ventral petrosal sinus'''. The cavernous sinuses lie on either side of the pituitary gland on the floor of the cranial vault.  They are joined across the midline by the cranial and caudal intercavernous sinuses to encircle the pituitary. This circle of sinuses around the pituitary has connections through the '''orbital fissure''', the '''optic foramen''', and the '''oval foramen''' to peripheral veins. The internal carotid artery lies within this sinus system in the horse.  Caudally, the cavernous system

The '''ventral sinus system''' contains the '''cavernous sinuses''', '''basilar sinus''', and '''ventral petrosal sinus'''. The cavernous sinuses lie on either side of the [[Equine Endocrine System - Horse Anatomy#Pituitary Gland|pituitary gland]] on the floor of the cranial vault.  They are joined across the midline by the cranial and caudal intercavernous sinuses to encircle the [[Equine Endocrine System - Horse Anatomy#Pituitary Gland|pituitary gland]] . This circle of sinuses around the [[Equine Endocrine System - Horse Anatomy#Pituitary Gland|pituitary gland]]  has connections through the '''orbital fissure''', the '''optic foramen''', and the '''oval foramen''' to peripheral veins. The internal carotid artery lies within this sinus system in the horse.  Caudally, the cavernous system

communicates with the '''basilar sinus''', which lies on the floor of the occipital bone, and the '''ventral petrosal sinus''', which lies within the dura mater in the caudal part of the cranial vault. The

communicates with the '''basilar sinus''', which lies on the floor of the occipital bone, and the '''ventral petrosal sinus''', which lies within the [[Equine Meninges - Horse Anatomy#Dura Mater|dura mater]] in the caudal part of the cranial vault. The '''ventral petrosal sinus''' exits the '''foramen lacerum''' or '''jugular foramen''' to become continuous with the '''jugular vein'''.

'''ventral petrosal sinus''' exits the '''foramen lacerum''' or '''jugular foramen''' to become continuous with the '''jugular vein'''.