Complex sentence: It divides, opposite the third sacral vertebra, into two branches, which descend one on either side of the rectum, and about 10 or 12 cm. from the anus break up into several small branches.
Split into simpler sentences: It divides, opposite the third sacral vertebra into two branches, which descend one on either side of the rectum. About 10 or 12 cm from the anus, these branches break up into several small branches.