Longitudinal ultrasonogram of the vertebral canal. Longitudinal ultrasonogram of the vertebral canal in a 4.6-year-old Swiss Braunvieh cow at the level of the atlanto-occipital space immediately after euthanasia. Left is cranial and right is caudal. a Distance between skin and arachnoidea, b Dorsal compartment of the subarachnoid space, c Spinal cord, d Ventral compartment of the subarachnoid space, 1 Atlanto-occipital membrane, 2 Central canal, 3 Atlas, 4 Skin, 5 Nuchal ligament, 6 Major rectus capitis muscle, 7 Minor rectus capitis muscle