Spinal cord segments. B. Gross structure in the adult monkey

Abstract

Abstract Dorsal and ventral roots were dissected bilaterally on spinal cords of adult monkeys: six rhesus, six irus and three baboons. Measurements made were: the distance between the uppermost cord attachments of successive nerve roots (segment length); the distance between the uppermost and lowermost fila within each root (root attachment length); and the distance beween the lowermost fila of one root and the uppermost fila of the subjacent root (interroot length). Segment lengths, dorsally and ventrally, are essentially alike within each species. In rhesus the average at various levels ranges from 4½ mm in cervical and sacral to 12½ mm in lower thoracic; in irus, from 4 mm in cervical and sacral to 10 mm in lower thoracic; in the baboon, from 5½ mm in cervical and sacral to 19 mm in lower thoracic. Within each species the dorsal and ventral root attachment lengths are similar, as are the interroot lengths, except in the lower thoracic levels. There dorsal interroot lengths range up to 3 mm longer than ventral. Cross sectional areas of the various levels were planimetrically determined. Within each species the largest areas are at lower cervical and lower lumbar levels. Individual segment volumes were calculated. In rhesus and irus these vary only about 60 mm 3 from the largest to the smallest segment, excluding sacrocaudal levels. In baboon this difference is as much as 260 mm 3 .