The distribution of the lumbosacral posterior rami and the sinu-vertebral branches (ramus meningeus) of spinal nerves was determined by dissection of newborn and adult cadavera and by a detailed study of serial sections of human foetuses. In addition, blood pressure and respiration were recorded and electromyograms were made in decerebrate cats during electrical and mechanical stimulation of low-back structures.

The posterior rami, in addition to their cutaneous and muscular distribution, give sensory fibers to fascia, ligaments, periosteum, and intervertebral joints. Adjacent divisions overlap in their area of supply. Interspinous ligaments are supplied mainly by branches from the next cranial level. Sinu-vertebral nerves supply posterior longitudinal ligament, dura mater, periosteum, and blood vessels, show intersegmental anastomoses, and contain sensory fibers.

Painful stimulation of joints and ligaments of the lumbosacral region in cats produces reflex spasm of dorsal and hamstring muscles, as well as non-specific changes in respiration and blood pressure.

It is suggested that clinically a painful stimulus to any deep structure in this region is poorly localized and can give rise to a common symptom complex which includes both low-back and leg pain.