The walls of the bony vertebral canal are formed by parts of the vertebrae: the anterior border comes from the vertebral bodies (with the intervertebral discs between adjacent bodies helping define the boundary), the lateral aspects are formed by the pedicles, and the posterior wall is built by the laminae of the vertebral arches. The intervertebral disc itself is a cartilaginous pad between vertebral bodies, not a bone, so it does not constitute a bony border of the canal. That’s why the disc is the structure that does not form a border of the bony vertebral canal.

Regulation of blood pressure and respiration is controlled by centers in the medulla oblongata. The cardiovascular center in the medulla adjusts heart rate and vascular tone to keep blood pressure within narrow limits, while the respiratory rhythmicity center produces the basic breathing pattern and tweaks rate and depth in response to chemical signals. It receives input from baroreceptors and chemoreceptors to maintain proper gas exchange and blood chemistry. The pons can modulate breathing, but the medulla houses the main centers for BP and respiration, making it the best answer. The cerebellum coordinates movement and balance, not autonomic regulation, and the thalamus mainly relays sensory information rather than controlling vital autonomic functions.

Imbrication is the term for the overlapping of dorsal spinous processes along the horse’s spine. When the cranial spinous process overlaps the caudal one of the adjacent vertebra, this pattern is described simply as imbrication. Since the description doesn’t mention any change in the angle or direction of the processes, it’s imbrication only. If an angular change were present, you’d describe it as imbrication with angular change. Cranial overlap or caudal overlap describe direction, but the standard term for the overlapping arrangement itself is imbrication.

Hands are a traditional unit used to measure horse height, with one hand equal to four inches. So the measurement in inches for a hand is four inches. In practice, horse height is written in hands with optional inches (e.g., 15 hands 2 inches equals 62 inches tall).