ARTERIES

 

The blood supply to the forebrain and midbrain comes from the circulus arteriosus cerebri[1] also known as circle of Willis. This surrounds the hypophysis and the optic chiasm on the ventral surface of the encephalon. In the dog, two arteries supply the circulus: the basilar artery and the two internal carotid arteries. The hindbrain receives blood from branches of the basilar artery.

 

The basilar artery is a rostral continuation of the ventral spinal artery. In its course on the ventral aspect of the medulla oblongata, branches off the caudal cerebellar artery, the labyrinthine artery and pontine arteries.  In the cat, this artery does not supply the circulus as the flux of blood is rostrocaudal.

 

The internal carotid artery enters the caudal carotid foramen through the tympano-occipital fissure to run in the carotid canal to leave through the external carotid foramen, makes a loop and reenters the cranial cavity through the internal carotid foramen. It receives the ascending pharingeal arteri before reentering the cranial cavity. In the cat, the internal carotid artery is occluded. However, intracranially, there is an internal carotid artery that receives blood through the ascending pharyngeal artery (via the carotid foramen), and from the rete mirabile (of the maxillary artery) via the orbital fissure.

 

In cats, the internal carotid artery is occluded. However, intracranially, there is an internal carotid artery that receives blood through the ascending pharyngeal artery (via the carotid foramen), and from the rete mirabile (of the maxillary artery) via the orbital fissure.

 

The rostral cerebral artery is a terminal branch from the internal carotid artery. It forms the rostral part of the circle of Willis. It courses dorsally to the optic chiasm, surrounds the genu of the corpus callosum and continues along its dorsal surface to anastomose with the caudal cerebral artery. Arterial bridges may be present between the left and right rostral cerebral arteries. An important one is the rostral communicating artery, located rostrally to the optic chiasm. Other bridges may be present at the level of the genu of the corpus callosum. The rostral cerebral artery supplies the medial cortical surface of the frontal cortex, the cingulated gyrus and the gyri bordering the longitudinal fissure on the rostral two thirds of the surface of the cerebrum. The internal ethmoidal artery and the internal ophthalmic artery are branches of the rostral cerebral artery. The internal ethmoidal artery reaches the cribriform plate of the ethmoidal bone where it anastomoses with branches of the external ethmoidal artery. The internal ophthalmic artery follows the optic nerve through the optic canal to the orbit where it anastomoses with branches of the external ophthalmic artery.

 

The middle cerebral artery is the largest artery of the brain. It is a branch from the cerebral arterial circle close to the internal carotid artery (some authors point out that the middle cerebral artery is a terminal branch of the internal carotid artery). Courses on the lateral surface of the cerebral hemisphere to supply. Near its origin, it gives rise to the rostral choroid artery. This artery may also be a branch of from the caudal communicating artery, near the origin of the middle cerebral artery. The rostral choroid artery enters the lateral ventricle near its origin and supplies the choroid plexus of this ventricle. The striated arteries leave the middle cerebral artery near its origin to supply the basal nuclei and internal capsule. Patological disturbances of the striated arteries may not result in hemiplegia but may cause compulsive circling towards the side of the lesion.

 

The caudal cerebral artery arises from the caudal communicating artery, rostrally to the oculomotor nerve. It courses over the ventral surface of the crus cerebri to continue, dorsolaterally, to the cerebral peduncle. Just after branching from the caudal communicating artery it divides in a rostral branch and a caudal one. The rostral branch runs between the optic tract and the medial geniculate body to reach the roof of the third ventricle and the splenium of the corpus callosum where it sends branches to the occipital cerebrum and it anastomoses with the rostral cerebral artery. In its ascending course, surrounds the lateral geniculate body, and gives rise to the caudal choroid artery. This artery supplies blood to the pineal gland, the choroid plexus of the third ventricle, the geniculate bodies, the brachium of the rostral colliculus and medial surfaces of the thalamus (Page 1769 of "The anatomy of the domestic animals" by S. Sisson and J. D. Grossman 5th ed.). The caudal cerebral artery branches off to supply the medial surface of the caudal part of the cerebrum and the gyri that border the longitudinal fissure on the caudal one third of the dorsal surface of the cerebrum. It also supplies the diencephalon and the rostral mesencephalon.

 

The rostral cerebellar artery is a branch from the caudal communicating artery. It courses caudally to the oculomotor nerve, and dorsocaudally along the lateral surface of the pons and the middle cerebellar peduncle to supply the rostral half of the cerebellum and the caudal mesencephalon.

 

The caudal cerebellar artery is a branch of the basilar artery at the level of the medulla oblongata. It is located rostrally to the rootlets of the hypoglossal nerve. It courses dorsally, along the lateral surface of the medulla oblongata and the caudal cerebellar peduncle, to vascularize the caudal half of the cerebellum. After passing caudally the caudal cerebellar peduncle, gives rise to the choroid plexus of the fourth ventricle.

 

Pontine branches and the labyrinthine artery originate from the basilar artery at the level of the pons and trapezoid body respectively.

 

The dura mater is vascularized by the rostral, middle and caudal meningeal arteries. The rostral meningeal artery is a branch of the external ethmoidal artery close to the cribiform plate inside the cranial cavity. The middle meningeal artery is the most extensive meningeal artery. After branching from the maxillary artery, enters the cranial cavity through the oval foramen, runs caudosorsally and bifurcates into rostral and caudal branches. It supplies the dura mater that covers the temporal and parietal cortices. The caudal meningeal artery is a branch of the occipital artery that enters the cranial cavity through the mastoid foramen. It supplies the dura mater of the dorsocaudal cranial cavity and the tentorium cerebelly.

 

[1] Described by Johan Vesling in 1647 and named by Thomas Willis in 1664.