SENSORY NERVE-ENDINGS IN THE ANAL-CANAL - INCREASING PATTERNS WITH AGE

Eleven fetuses and 9 newborns were examined for sensory innervation of the anorectal area. The specimens were obtained immediately after dea th and were stained by the modified Gross silver impregnation method a nd examined with a light microscope. The perianal skin and rectal muco sa did not differ in either group. The anal canals of the fetuses had numerous thin, singly- and doubly-branched nerve endings with 1.0 to 1 .5 mum axonal diameters. Paccinian-type lamellated corpuscles were few and contained 3-5 fibroblastic lamellae and had a diameter of 70-100 mum. The newborn group had more prominent subepithelial free nerve end ings with 2.0 to 2.5-mum axonal diameters, mostly myelinated and with numerous Paccinian corpuscles with 8-10 lamellae and diameters of 100- 150 mum. Globular endings were fewer and smaller in the fetal group. M uscle spindles were seen embedded in the external sphincter muscle bun dles of both groups. We conclude that this pattern of sensory nerve en dings indicates a time-dependent developmental process in the human an al canal.