A neonate does not pass meconium until 48 hours after his birth. Two weeks later his mother reports that he has not been passing stool regularly. Anorectal manometry reveals increased internal anal sp

A neonate does not pass meconium until 48 hours after his birth. Two weeks later his mother reports that he has not been passing stool regularly. Anorectal manometry reveals increased internal anal sphincter pressure on rectal distention with a balloon. Radiographic studies reveal massive dilation of the colon proximal to the rectum. The findings in this case indicate a developmental abnormality of which of the following embryonic tissues?