The pectinate line indicates the junction of
the superior part of the anal canal and the inferior part. The anal canal superior to the pectinate line differs from the part inferior to the
pectinate line in its arterial supply, innervation,
and venous and lymphatic drainage. The superior rectal artery supplies the superior part of
the anal canal and the inferior rectal arteries
supply the inferior part. Superior to the pectinate line, the internal rectal venous plexus
drains chiefly into the superior rectal vein—a
tributary of the inferior mesenteric vein and the
portal system. Inferior to the pectinate line the
internal rectal plexus drains into the inferior
rectal veins—tributaries to the caval venous system. Superior to the pectinate line, the lymphatics drain into the internal iliac lymph nodes into
the common iliac and lumbar nodes. Inferior to
the pectinate line, the lymphatics drain into the
superficial inguinal lymph nodes. Superior to
the pectinate line, the innervation is visceral;
inferior to the pectinate line, the innervation is
somatic