The anatomy of the arterial supply to the cranial regions of the sheep and ox

By means of neoprene latex injected preparations, the anatomy of the arterial supply to the brain has been determined in the sheep and ox. In these two ruminant species, blood destined for the Circle of Willis and thence the brain must first pass through a well‐developed intra‐cranial carotid rete. The main source of blood supply to the carotid rete in the sheep is from the external carotid artery, via branches of the internal maxillary artery. In both the sheep and the ox, the internal carotid artery is poorly developed in the young animal and the portion proximal to the carotid rete is absent in the adult. The internal carotid artery, in animals of all ages, can be traced through the rete to emerge as the efferent vessel, which divides to form the Circle of Willis. In the ox, the main source of blood supply to the intra‐cranial carotid rete is the external carotid artery, via branches of the internal maxillary, but, in addition, the rete communicates directly with the vertebral arteries by way of the basi‐occipital arterial plexus. Unlike most other species, the basilar artery in both sheep and ox has only tenuous connections with the vertebrals. In both species, the basilar artery tapers caudally and is continued as the ventral spinal artery. The basilar can therefore be regarded as a caudally directed branch of the Circle of Willis in both these animals. A well‐developed occipito‐vertebral anastomosis is a marked feature of the cephalic circulation in both sheep and ox.