Transverse process [Atlantal wing]

The transverse processes are expanded and project laterally of each masses, forming shelf-like processes termed the wing of atlas. Each wing is hollowed to form the atlantic fossa on their ventral surface (especially deep in horses, flat in dogs). The base (cranial part) of each wing is perforated by the alar foramen (absent in carnivores, replaced by the alar notch) for passage of vertebral artery.