Complex sentence: After attending school in Aberdeen, he was sent by his guardians to Dundee, attending the High School of Dundee and was then apprenticed to a pharmacist; upon returning to Aberdeen he began his medical studies in the University there.
Split into simpler sentences: After attending school in Aberdeen, he was sent by his guardians to Dundee, attending the High School of Dundee and was then apprenticed to a pharmacist. Upon returning to Aberdeen he began his medical studies in the University there.