The mother of a two-month-old baby complains that her baby i…
The mother of a two-month-old baby complains that her baby is constipated, has a bloated abdomen and has been vomiting quite frequently lately. The baby has lost weight since the last visit. Upon examination you note the baby’s belly is quite distended with noticeable stool in the colon, though the rectum is empty. A barium enema imaging series shows a markedly constricted terminal bowel. A biopsy of the rectum shows an absence of the parasympathetic ganglia in the rectal wall. A defect in the development of which of the following could best account for this condition?